handloads exceed max OAL - safety issue?

[d94jonca]

hi all,

ive been handloading for economy for several years, but have lately started to see what i can do to improve accuracy as well. after having read an article on this subject, i created a batch of cartridges where the bullet is seated "shallowly" so as to have the bullet almost touch the lands when the cartridge is chambered.

the cartridges chambers easily (and their oal does not change in this process) but they definitely look funny, with the crimp groves being some 4 mm (ca .16 inch) above the edge of the case.

however, what does concern me is that the OAL of these loads exceed the maximum OAL as specified in my reloading manual. do you guys know if there are any safety issues with this, or if the maximum OAL is only there to make sure the cartridge will fit in standard magazines, cycle properly etc?

btw its a rem 700 adl chambered in 7mm rem mag, the bullet in question is a 154 gr hornady sst.

thanks!

[918v]

If you seat the bullet deeper, you will reuce case volume and increase pressure. If you seat the bullet long, you will increase case volume and decrease pressure. Reloading manuals warn about seating too shallow to avoid creating an excessive pressure situation. Don't worry about seating long.

[Unclenick]

SAMMI OAL specifications are intended to ensure cartridges fit in standard magazines, not for pressure safety. The exception is that increased pressure is observed when the bullet is actually touching the lands. This is because the bullet gets no running start into the rifling. To start the bullet moving, the combustion pressure then not only has to expand the case neck, but swage the bullet into the rifling to move it. The result is a slight delay in the bullet's initial motion, so the case capacity remains fixed a bit longer and start pressure is increased. If you are approximately 0.020" (or 0.5 mm) or more deeply seated than touching the lands, you are unlikely to see much of this effect. If you are closer to the lands than this, it is worth backing the load down to a normal starting load and working it up again just to be safe. Other than this exception, as 918V said, increasing case space decreases pressure.

Anymore, I usually take a starting load intended for a standard length load, seat to touch the lands, shoot a group, then try groups with bullets seated deeper in 0.01" (.25 mm) increments until I find the seating depth that produces best accuracy in that gun. After finding that seating depth, I work the powder charge up to find what charge improves that accuracy most?

Nick

[Jim Watson]

If you had a maximum powder charge and a bullet rammed into the rifling, it might give excessive pressure. If you have any "jump" at all, you are ok. Longer is usually better for accuracy.

[d94jonca]

thanks for the clarifications! im looking forward to try these babies!

[amamnn]

Internal ballistics is a subject that is endlessly fascinating and a source of endless contention. This is because the field is largely theoretical. We can vary certain aspects of a cartridge and observe the results, but when it comes to explaining why something happens, or exactly how, we are pretty much in the same boat with vulcanologists trying to predict when Mt. St. Helen's is going to explode again, or if Yellowstone will kill us all next week.
You can look in Hornady's very good reloading manual " Handbook of Cartridge Reloading volume 1, second edition" and read the statement that "If bullets are seated too deeply, they have a longer distance to travel unsupported to reach the bore, and may enter it off-center" page 63.
You will note that they are talking about bullets seated too deeply and they go on to state that in general less distance = better accuracy. You can also look in Richard Lee's very good book "Modern Reloading volume 2" you can find information about seating near the lands that states " Few people know the reason........it Provides uniform start pressure." page 56. You can fine quotes enough to fill 50 posts on this subject, but you will not find any responsible author telling you that seating on the lands is a cure-all for accuracy or even a good idea. In fact, reduced leade A.K.A. freebore A.K.A. that little distance from your bullet's widest point to where it actually contacts the lands, can be a cause of overpressure. This was at the heart of the 5.56mm vs. .223 rem controversy of days gone by. http://www.thegunzone.com/556v223.html#nb1
The statement that benchresters seat on the lands is a distortion and just not true. Benchrest shooters try to seat the bullet at the closest point to the lands where accuracy is the best. This is not to say ON the lands. In fact, with changes in the humidity and barometric pressure, the sweet spot may vary. This is why we take many boxes of ammo to the match. The load seated at .010" off the lands that won last month may not work today--it may require .020" off the lands today.
Another very interesting experiment performed by Richard Lee, which concerns pressure/ bullet depth/ freebore can be read on pages 112 - 113 of his book. His results might be surprising to many.
The bottom line is that you need to experiment with bullet seating to find the sweet spot for your rifle/load and not be surprised if it shoots differently in July than it did in January, or on a rainy day, or etc. etc. Also keep in mind that if you actually find the holy grail of reloading: the perfect cartridge, you have fixed only one third of the accuracy triad. In my opinion, less than a third as I give more weight to the shooter than the rifle and more weight to the rifle than the ammo.

[MrApathy]

before doing so see how much free bore you have above the chamber.

make a test cartridge with no powder or primer marker up the bullet or paint it or light a fire and put the bullet over the smoke and let carbon buildup on the bullet. then chamber it see if you hit rifling.

lots of people on brianenos forum use 40sw and load it to 10mm lengths. reduces pressure and functions better in 1911 pattern guns designed for use with 45acp bullets which are good amount longer than 40sw with 1.135" max.

[RERICK]

I also am having an issue regarding longer than mormal oal.I picked up the Stoney point oal gauge and I measured my chamber for oal on a Hornady
75 grain A max. I was getting horrible groups at the specified oal which is
2.330 and then measurement I got was an average of 2.435.In fact most of the bullet types were longer than specified.So if i am hearing right I could seat at say 2.410 without any danger of high pressure? The Gun is a Remington 700P in .223

[Smokey Joe]

Rarick--The short answer is yes, but.... The longer answer is the one Mr. Apathy gave--You have to find out what the max length with a PARTICULAR BULLET is in YOUR CHAMBER, and then load to a shorter max length than that.

If you then load for a second rifle, or want to try another model or weight of bullet, you have to do the max length testing all over again. Every different bullet will have a slightly different ogive (curve shape from cylindrical forward to the bullet's point) so every bullet will have a different max length, even in the same rifle.

A further complication: As yr rifle ages, it experiences "throat wear" which means that it will take a longer and longer cartridge OAL over time to get the bullet that magic "perfect" distance from the lands.

Anyhow, the SAAMI OAL specs are just to ensure that all commercial bullets function in all magazines and all chambers. If yr rifle tests OK with a longer OAL, that's fine. You may very well have magazine feeding issues with a longer OAL that yr rifle shoots very accurately--that's OK, just single-load the cartridges, and when you want to use the magazine, hunting for example, use a shorter OAL.

I say again, though, just for caution's sake: CHECK the OAL for a given bullet in YOUR rifle, then load it slightly shorter.

[Unclenick]

Go back to what Amamnn said. This is very gun dependent. I'll throw a examples into the kitty:

At the long range firing school at Camp Perry, Middleton Thompkins explained that he does all the loading for himself and his family, all of whom continue to shoot in the top ranks at long range (except that Mid himself is semi-retired from competition). He resizes his necks wide, so the bullets can be moved by finger pressure alone. He leaves them too long and allows closing the bolt to finish seating the bullet by pressing it against the lands. Definitely touching. The reasoning? Due to the arc in trajectory at long range shot-to-shot velocity variation has a lot of effect on vertical POI, while at short range it is often imperceptible or compensated for by difference in muzzle rise. This seating method appears to produce the least standard deviation in MV, per the comments by Richard Lee. That Thompkins gives up employing case neck tension doesn't seem to matter. Perhaps it is helpful, as that tension can vary a good deal (see the second photo in this information on the RSI LoadForce-250 tool to see a distribution).

This last point ties into the observation by pistol shooters going back 20-odd years that military pistol match ammunition was consistently more accurate than commercial equivalents. It was ultimately determined that the pitch used to seal the bullets caused start pressure to increase. Apparently that improved ignition uniformity enough to be visible on the target.

In any event, there are at least those three ways to skin the start pressure uniformity cat (land seating, seating force measurement, pitch sealant).

Another is something I've seen posted in at least three places in discussions related to Audette Ladders. It describes a Somchem program that once existed to help customers find the best loads for their rifles. They once got an old Mauser 8x57 with a throat so badly worn that they were certain it would never shoot well again. At the customer's request, they nonetheless tried. They seated the bullets progressively deeper until suddenly the groups tightened. They then adjusted the powder charge and wound up with a gun shooting 6.5 mm (.257") C-T-C at 100 meters. The most accurate Mauser hunting rifle they had ever had. One location is here.

For general information, running theoretical calculations in QuickLOAD for cartridges in the .308 case capacity range (175 gr SMK, 42.3 gr. H4895, LC case), increasing seating depth by 0.01" causes a pressure increase approximately equal to adding 0.1 grains of powder. This does not take into account the effect of a bullet touching the rifling.

"...there is always a well-known solution to every human problem - neat, plausible, and wrong." H. L. Mencken

It all comes down to individual gun and ammunition combinations. There is no rule that seems to prove true in all cases, so dust off the loading gear and get your hands dirty. And stay safe.

Nick

[918v]

Anytime you seat deeper, pressure goes up. That is a fact. If you load to maximum pressures right at the lands, then begin to decrease seating depth to find the sweet spot, you will increase pressure over max. That is never a good idea.