Overall bullet seating for .270

Discussion in 'Ammunition & Reloading' started by 66goat, Jan 28, 2012.

  1. 66goat

    66goat Member

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    Hello, I recently purchased a Hornady OAL gauge and was trying it out the first time tonight on my S&W 1500 .270. I measured multiple times with the OAL gauge and bullet comparator on the calipers and was getting consistent results (2.929, 2.923 and 2.923) when using Sierra 130gr BT. I came up with an OAL of 3.393 allowing for 0.030 off of the rifling. My question is, does this seem excessive in length? The Sierra manual lists an OAL of 3.300". Curious how much OAL can vary from what is listed in the manuals when using a OAL gauge.

    Thanks
    Matt
  2. Gunner3456

    Gunner3456 Well-Known Member

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    I'm not sure how you know you are .030 back of the rifling. Did you load long until it touched, and then back off .030?

    Different bullets have different shapes and will contact at different lengths. I load .270 but not that bullet, so I can't say.

    If you know you're back .030 and you're only long by that much, I wouldn't worry about it. My only concern would be that I don't like .030 much. I'd rather see a max of .020. I'd be going to a really good gunsmith to have may chamber measured, and talk to Sierra to see if I could load that bullet longer, and then make a decision what to do. Be sure to measure your case lengths before you talk to Sierra.
  3. Spitpatch

    Spitpatch Bronze Supporter Bronze Supporter

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    Well, the short answer (resulting in a long solution), is that each gun will prefer a different OAL for the cartridge, and if you change bullets, the preferred OAL will change too. There is no such thing as "excessive OAL", as long as the bullet is seated sufficiently in the case to reduce chances of non-concentricity, the cartridge operates from the magazine, and rifling is not excessively engaged by the bullet upon chambering. Gunner's max of .020 away is a good base point, and if you are not loading at the top end of pressures, some guns prefer the bullet to actually just touch the rifling. The old method, before gadgetry such as "cartridge comparators" became prevalent was "painting" the exterior of the bullet with a magic marker, find the OAL that DOES show indications of rifling engagement, and shorten OAL incrementally until no rifling marks are shown on the "paint". Further experimentation from this OAL for that particular gun might grant improvement in accuracy. Back then, we didn't ever really know exactly how far our bullet was away from the rifling, but we did know exactly what OAL our gun liked for that bullet. Handloaders of today can still be well served by this method. A comparator grants us one more number (referencing on the ogive), and considers the fact that OAL of the BULLET may not be precisely identical, bullet to bullet, even from the same box (especially with softpoint bullets). I would submit that ogive might be minutely variable as well.

    A word concerning "cartridge operates from the magazine": Make sure your cartridge length allows for function with a FULL magazine. Sometimes a cartridge that goes into the magazine just fine by itself might be an OAL that would malfunction if the magazine were full.
    Gunner3456 and (deleted member) like this.
  4. Gunner3456

    Gunner3456 Well-Known Member

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    Very good post. :thumbup:

    The part I quoted is why I suggested he measure his case length before he asked Sierra about OAL. They will want to be sure the bullet is adequately seated in the case.

    Again, I haven't used that bullet, but I'm puzzled as to why he can't get closer than .030 and would want my chamber measured. I'm with you. I seat just back of the riflings, and .020 would be max for me.

    The .270 tends to be very accurate and I'd want to work up a good load for it, and not be limited to .030 even if I had to get different bullets. I do like the 130gr for all things .270, and haven't had his issue.

    FWIW, I use Remington PSP bullets in 130gr for everything in my .270.
  5. Spitpatch

    Spitpatch Bronze Supporter Bronze Supporter

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    My rule of thumb for "seating sufficiently", is that I like the bullet to engage the interior of the neck to a depth at least that of the diameter of the bullet. (For a flat-base .270, this would be at least .270 into the neck: for a .224 bullet, .224" of engagement.) Boattail bullets dictate we disregard that portion of the bullet (the boattail) not contacting walls of the neck when measuring this.

    Another word of caution is toward cartridge durability outside the gun. For a rigorous big-game hunt, where cartridges might be jostled in pockets and such, we might consider an increased seating depth, as opposed to a foray in the dogtown where our cartridges stay in a plastic segmented box until just before they go into the gun.
  6. Gunner3456

    Gunner3456 Well-Known Member

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    Bullet depth can also be affected from recoil if they aren't sufficiently seated in the case neck. This is while they are in the gun, in the magazine, while you're shooting.
  7. Jamie6.5

    Jamie6.5 Well-Known Member

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    Both of my .270 barrels have notoriously long throats (leade, freebore).
    I recently bought some Sierra 135gr HPBT match bullets to give them a try, and due to the ogive shape, I can't get them to the lands before they won't stay in the casing.
    I was told by my gunsmith that most factory .270 chambers are throated that way so that, should someone try the old 160gr round nose ammo, that they won't be jammed in the lands.
    I happen to have a couple of those rounds, and the OAL using my Hornady comparator is waaay out there.
    He recommended a minimum of 2/3ds bullet diameter of the bullet's bearing surface be seated in the neck. With hunting loads I prefer the one diameter rule Spitpatch outlined above.

    When I use 150gr Interbonds or SSTs though, I can get them out there far enough to gain some case capacity for max loads, and they still fit in the mag.
    After reading Bryan Litz's instructions for seating depth using Bergers, I start my hunting loads with an .080 jump, and adjust OAL for fine tuning.
    Tossing out factory and book OALs has led me to use 150gr bullets almost exclusively. There is just too much gained, and not enough reason to use the lesser BC 130s.
  8. Gunner3456

    Gunner3456 Well-Known Member

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    This is another debate which will never end, LOL. The .270 works well with a 150gr bullet. I subscribe to the other school of speed overcomes weight and gives equal or better performance in terminal ballistics and trajectory at all ranges.

    For instance, if it wasn't for speed, the little 5.56 wouldn't be a battle rifle.

    I'm not trying to change anyone's mind, especially since I know only how my particular gun works best.

    "The load that made the .270 Winchester's reputation was the 130 grain spitzer bullet at a muzzle velocity (MV) of 3140 fps. The recoil energy from firing this load in an 8 pound rifle amounts to 16.5 ft. lbs. This level of performance can still be achieved by the reloader.

    Today's standard factory loads drive the 130 grain spitzer to about 3060 fps. The Speer 130 grain flat base spitzer has a ballistic coefficient (BC) of .408, and a sectional density (SD) of .242; the 130 grain boat tail spitzer has a BC of .449. These numbers are right in the big game ballpark. And because the 130 grain .270 bullet is fast, it hits hard. Factory energy figures look like this: muzzle energy (ME) of 2705 ft. lbs., 100 yard energy of 2226 ft. lbs., 200 yard energy of 1817 ft. lbs., 300 yard energy of 1468 ft. lbs., and 400 yard energy of 1175 ft. lbs."


    (And reloads at the old 3150 fps hit harder.)

    .270 Win.
  9. Jamie6.5

    Jamie6.5 Well-Known Member

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    Yeah I know Gunner.
    The 150gr Interbond (.525 BC) leaving the muzzle @2950FPS (RL17) gets to 400 yds with over 2200fps of velocity, and over 1700 ft/lbs of energy.
    Like the 130s do at 250 yards.
    When it gets to 500yds, it still has more energy than the 130 does at 300yds
    The 150gr .270 bullet has the same S.D as a 180gr .30 cal bullet and penetrates like one too.

    Don't get me wrong, I shot 130s for years, and the biggest mulie I ever killed was at 320 yds, with one shot. He took two stumbling steps and died. A Rem130gr core-lokt did the deed.
    But I have since moved on.
  10. Gunner3456

    Gunner3456 Well-Known Member

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    No argument. I use the 130gr Rem core-lokt psp. We have different guns and mine doesn't like the 150 as well but yours does. I can't for the life of me get the best accuracy with the 150, no matter what I try and believe me, I've tried. It appears that you can.

    Every animal I've shot since 1974 in E. Oregon, Montana and Wy. has gone down, including elk and one bear.

    On the other hand, a friend who swore by his 300 Win Mag flinched when he shot it. He hit a nice muley in the hind quarters at about 250 yds and the poor deer was up on its front legs trying to go. I finished it with my .270. I don't know if that was legal for me to do, but it had to be done.

    Sounds like you have a really good rifle. I picked mine up when it was like new but one year old in 1974. It's a "tang safety" Ruger M77. Would you believe that back in the day, I paid $200 for it used, and it had a fine Leopold 2x7 Gold Ring scope mounted and included?
  11. Jamie6.5

    Jamie6.5 Well-Known Member

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    That is why my next .270 barrel will have an Ackley chamber and a custom throat. I have a friend with one that shoots 150gr Accubonds at over 3100fps, and prints around/under 1" groups at 200yds.
    That is 130gr territory for velocity, and though I have eaten the results in the form of elk steaks, I have to take his word for it that it is a VERY lethal combo.
    He zeros it at 275yds, and claims he holds dead on out to 325yds or so.

    Either that or I will step up to a .280 Ackley and convert a bunch of my .270 brass.
  12. 66goat

    66goat Member

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    Wow, talk about a wealth of replies and information...thanks all. As far as setting at .030, I was just going off the instructions from the Hornady OAL gauge of 0.020 to 0.040. I would prefer to be closer as long as the OAL still works.

    I am going to start fresh today and see if I have the same measurements. Currently this is more for messing around with some trail boss load than hunting rounds so I am not to concerned about having multiple rounds in the magazine.
  13. GRingle

    GRingle New Member

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    Excellent topic. I did a test on my 7mm Mag using 139 gr SST to determine the maximum OAL of 3.427". For this SST Hornady recommends 3.290". I used a fired case and a projectile snugged long into the case. I loaded this into the rifle and carefully closed the bolt. I then extracted this without letting the round get jostled around. I repeated this multiple times to determine a very consitent OAL. If I follow the thought above that i use a jump of 0.020" then I would seat this particular round at 3.407" which is almost 0.117" longer than recommended. Not sure this is correct. Am i missing something in this test?
  14. Spitpatch

    Spitpatch Bronze Supporter Bronze Supporter

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    Seating bullets to a "recommended" measurement of leap to the rifling (or a recommended no leap at all) makes absolutely no sense, other than to supply a (huge) ballpark figure that worked for the recommendor. To the recomendee, it could very well be so much pie in the sky.

    There are general rules of thumb that have worked well for some, and once again, these general rules of thumb might allow you to arrive in the parking lot of the ballpark. What I am trying to convey is that EACH GUN is different. EACH BARREL is different (even from guns of consecutive serial number spit from the bowels of a rifle/barrel factory the very same day). And, then, the moment we choose different brass, different powder charges, different primers, etc., etc., etc. ad nauseum, we negate all of our previous received recommendations. YOUR gun may like one load with the bullet just touching the rifling. Change the powder charge (or more significantly) the brass, and some measurement just off the rifling might be better.

    Seating depth to achieve a proximity to the rifling that improves accuracy should be amongst the very LAST of experiments to improve and fine-tune a load. So much more is to be gained with a different choice of bullet to start with, then powder, then primer (this is my own process of elimination based on what is most likely to produce the greatest amount of improvement).

    Yes, I do begin intial experimentation (in the bullet arena) partnering my bullet selection experimentation with one of the "parking lot of the ballpark" recommendations to seat closer to the rifling than a factory load would show. But I don't mess with it again until all else is settled, because there is so little to be gained when compared to all else. Yes, it is important. But there is a time when it BECOMES important, and that time is not initial load development.

    The greatest and most frequent trouble that is encountered by those believing (with great credence I would support) that "best accuracy is found with the bullet just engaging the rifling, or just off it", are also those that may find (once again with great credence in many cases) that "best accuracy is found with a maximum charge of powder that completely fills the case". Our handloading nimrod combines his two well-discovered techniques, pressures skyrocket (with or without his knowledge), and he becomes a high stakes gambler. He fails to take his experiments to the next stage, retain his power and velocity, back off his bullet from the rifling just a bit, and thereby achieve a safety margin of pressure (most often with NO decrease in accuracy).

    And apart from all of this, eventually all experimenters long in the tooth run into a good number of very good guns that shoot best with that darned bullet nearly a mile from the rifling when it starts its journey.
  15. deadshot2

    deadshot2 Well-Known Member

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    This axiom is a holdover from more simple times. One shooter found that the closer he put the bullet to the rifling the better his groups became. Another found that as he diddled with the powder loads, same effect. Some did both with great success.

    Then came better testing equipment and more technically trained people entering the sport of shooting and reloading.

    They discovered that in many cases the increases or decreases in load allowed the bullet to leave the muzzle at the optimum point in the barrel's harmonics. Then along came some research that showed OAL adjustment yielded similar results due to the altered "barrel timing" (amount of time the bullet was in transit from case to muzzle).

    Guess what, they're both important. However, just like when tuning anything else from an radio transmitter to a high performance engine, it's best to focus on ONE parameter until the results are maximized. Once near perfection is achieved with one, then move to the next and continue fine tuning.

    With hand loading I would suggest it makes more sense to START by finding the best powder load, one that is the most accurate, and using the "Factory" OAL for that given round. If for no other reason than it's a starting point. Once the best group has been achieved, then play with OAL until the performance has been optimized for that rifle.

    A good case in point, where "no jump" loads don't add to the accuracy of a rifle, or isn't practical due to huge amounts of freebore, are Remington 5R Milspecs with close to .200" of freebore and the Weatherby rifles that have long freebores so they can shoot those massive loads.

    Every handloader out there wants a shortcut. "What's your favorite load" seems to be the most asked question. Spitpatch hit it on the head that even consecutive rifle barrels with 100% of the same material, machine work, and handcrafting, will not perform equally. Close? Maybe, but not the same.

    Like it or not, every handload has to be started from the beginning if you want something more than what "just works".

    In closing, I frequently watch a couple of the best Benchrest Shooters the Pacific Northwest has grown when they develop a load.

    First it's a matter of finding the right powder load. Once the load is established they will then change OAL's, using the same load, by as little as .002" at a time until they obtain their trademark "one hole groups" that look like it was cut from the target using a fired case as a paper punch.

    To carry it to an extreme, some will even develop the "perfect load" for their rifle using a single case in order to remove that as a variable.

    No shortcuts, just lots of methodical adjustments.

    (sorry Spitpatch, I wasn't trying to write a longer post than yours, it just kind of kept coming out:laugh::laugh::laugh:)
  16. mjbskwim

    mjbskwim Well-Known Member

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    Happens all the time ,here in reloading.These guys are a wealth of knowledge.