7.7x58 length

[mustanggt]

I'm in the middle of prepping brand new PRVI brass for a type 99 that is on its way. I've never seen such consistent length in brass than these. They are all +/- .001". However they measure 2.275" which is 5 thou over max length per Hornady manual. I am using a sinclair ultimate trimmer and a 7x57 case holder that seems to be working well since they don't make or carry one specific to the 7.7x58. I'm wondering if there is a something I don't know about that would necessitate the over length cases? Any help is appreciated.

[Adam Helmer]

mustanggt,

WAIT until your 7.7MM rifle arrives and THEN let the rifle dictate what case length it prefers.

Adam

[mustanggt]

That's why I stopped at 5 cases because it kept nagging me while I was trimming. Thanks.

[Eddie2002]

Some of the 7.7 Arisakas have a worn throat and will take longer cases. I resize 30-06 brass for both my 7.7x58 rifles and have used brass 20 thousands over the specs with no trouble. I mainly use the longer brass for a 100 grain plinker round. Seems that the longer brass helps move the short boolit up closer to the rifling and improves the accuracy. Wait for your rifle and if the brass chambers with no problems then you are ready to go.

[mustanggt]

Thanks for the replies. Yes I'll wait for the rifle to see what it likes.

[curator]

mustanggt:

If you intend on shooting cast, the "extra" length may be a real benefit. Nearly all the 7.7 Arisakas I have done a throat slug on show chambers cut on the long side. They did this because ammo came from many sources and no one was worrying about reloaders 70 years into the future. Cases that reach to the very end of the chamber support the boolit better as it enters into the throat/leade. Short cases allow boolits to expand into the gap at the end of the case and then get swaged down again at the throat, allowing for some distortion and gas leakage. None of this is conducive to good accuracy. I make my 7.7Jap cases from .30-06 brass and cut the length to exactly fit my rifles' individual chambers. Like Eddie2002 says, 20+ thousandths over won't be unusual.

[mustanggt]

That's good to know. I'm glad I don't have to trim 150 cases. Not a fun chore. I'll let you guys know how it turns out when I get it in my grubby mitts.

[Safeshot]

To trim a "lot" of cases use a Lee Case trimmer and stud in a drill press. Set the Drill Press Quill to stop when the pin just touches the table. You can trim cases fast and accurate and trimming 150 or 200 cases is "FUN". Even trimming 30/06 cases resized to 7.7 x 58MM length takes only seconds each. Enjoy.

[Multigunner]

I once had a problem with some .30 Carbine ammo that caused a regular jam in one of every six shots.
I checked the fired cases and found that one in every six cases was .006 longer than the rest.

When I ordered Remington .303 cases by the hundreds I found these showed no sign of having been finish trimmed, the case mouths were uneven. I trmmed these and squared up the case mouths before using them.

[bruce drake]

Next time you need brass, you can easily make them out of 30-06 cases. Trim to max-length 58mm and then you reform the cases in the size just once it is a right size to make the shorter cartridge. Or if you have a ton of 8mm or 7mms around, just neck them down and you'll be just fine as there is only 1 mm difference in neck length.

[mustanggt]

I have a lot of 7x57 brass from load development last year for my first deer hunt. So that is good to know. Rifle should be showing up today. Thank you fellas.

[Multigunner]

Remember that military rifles have a small amount of slack in the chambers for good reasons.
Julian Hatcher found that when a Springfield bolt was operated as rapidly as possible the cartridge case could end up with the shoulder set back by as much as .006" just by inertia alone. The neck of course would be functionally about the same amount longer.

If the cartridge is trimmed to match the chamber neck length exactly theres no slack to compensate for this sort of shoulder set back so if the action were operated very quickly you might end up with the case mouth being crowded on firing, with a slight but noticeable increase in pressure.

If the case mouth is heavily crimped a cartridge would likely chamber easily even if the neck was too long. On firing the case mouth would be constricted as the neck expanded to release the bullet.
All that is unlikely to cause any serious problems , but bears thinking on.

Best to check case OAL after each firing just to be sure.

[EDG]

Military rifle chambers usually have a good bit to a lot of clearance at the end of the case mouth by design.
The only way to know how long the chamber is from head to case mouth is to measure it. Then you will know how long your cases can be.
I can assure you that you are not going to jam a standard length case in a loaded round into a chamber and pinch the end of the case mouth.

Based on my experience forming cases I don't think you will find a way to set back the shoulder of a .30-06 case .006" with the bolt regardless of what Hatcher said. You might do it with a machine gun but not a bolt gun.


Remember that military rifles have a small amount of slack in the chambers for good reasons.
Julian Hatcher found that when a Springfield bolt was operated as rapidly as possible the cartridge case could end up with the shoulder set back by as much as .006" just by inertia alone. The neck of course would be functionally about the same amount longer.

If the cartridge is trimmed to match the chamber neck length exactly theres no slack to compensate for this sort of shoulder set back so if the action were operated very quickly you might end up with the case mouth being crowded on firing, with a slight but noticeable increase in pressure.

If the case mouth is heavily crimped a cartridge would likely chamber easily even if the neck was too long. On firing the case mouth would be constricted as the neck expanded to release the bullet.
All that is unlikely to cause any serious problems , but bears thinking on.

Best to check case OAL after each firing just to be sure.

[pworley1]

I have never shot anything besides reformed 30 06 in any type 99. Most of it did not need to be trimmed.