powder blowback on a '92

[long colt lawrence]

Help!

My EMF Winchester 92 lever action repro blows back a nasty powder residue with each shot. I've been cryin' about it since yesterday. Actually I took my first shot without my safety glasses on and it feels like weld slag on my retina. Anyway, the gas is going past the casing and the ejector configuration throws it right in my face. Anybody else experience this? I'm new to reloading and I guess I'm sizing them too small which lets gas around the shell -or- my load isn't powerfull enough to expand the case and seal it off.

Any suggestions?

thanks

[The Shrink]

Lawrence

Post your load here and someone will give you a very good guess as to the pressures you're creating.  Unless you have a very large chamber, or are using a non-standard die, I'd guess that you are right about inadequate pressure.  

The other option would be an overlarge chamber.  Who makes the gun?  Can you do a chamber cast and measure it?

[long colt lawrence]

Thanks for the reply Shrink,

I should've given more info. Here's the specifics:
45 LC, unique powder 6-7.6 grains, 200 gr. roundnose., CCI primers

The reason I say 6 to 7.6 grains is that the auto measure cavity holds 7.6 gr. weighed on my scale, but yesterday random tests showed it varied down to +6 grains. I think this is because the powder is "flaky" and sometimes doesn't settle in the measure very dense (if that makes sense).

[richp41]

Lawrence, sounds like the pressure level in this load is too low to seal the case in the chamber and prevent blowby. The load you mentioned isn't even up to the pressure of a factory .45LC and that is pretty low. Try starting at 8.5 grs of Unique and increase til the problem disappears-- or switch to a faster powder that will generate more pressure faster.  Also make sure your chamber is dry of oil as oil allows some case slippage and leakage. Blowback is common in cartridges that develop under 25-30000# PSI and your load is probably in the range of 12- 15000#. This sealing affect is known as obturation and is needed to seal the case as well as prevent blowby of gas around the bullet and subsequent leading. Rich P

[Graybeard]

I believe what you are experiencing is a combination of two things.

1. A generously sized chamber which can be an asset in helping the rounds chamber.

2. The main cause. Low pressure not pushing the case out to seal it off. CAS folks all seem to want to use the very lightest pressure and velocity loads they can with the lightest bullets available. This is BAD NEWS. Low pressures fail to seal the gases off and let them blow by like that. I am of the opinion that if you are gonna use light weight bullets you need to drop down in bullet diameter accordingly so you can keep the velocity and pressure up enough to seal off the chamber and stop the blowby.

I've not shot my EMF 92 all that much yet and am not positive but I'm thinking both the Hornady and Black Hills factory ammo fail to seal off the gases. Reason I say this is about the right number to have been them were covered in blow by after my first match with it. Pretty sure it was the culprit not the EMF Dakotas I use.

My cure is to raise pressures enough to seal off the chamber from the gases.

GB

[Iowegan]

Had the same problem a few years back. Try annealing the top third of the case. This makes the brass soft so it puffs up and seals in the chamber. Shooting, resizing, and crimping work hardens the brass to a point where it doesn't expand and seal.  Annealing prolongs case life by about double in straight wall cases. I agree with the above, your load is pretty light. I would add a few grains of powder and apply a firm crimp for proper ignition.

[Castaway]

Ditto what the others said about the load being low pressure and not sealing the case mouth.  Up the charge (within the book of course) and you should see less carbon on the case mouth.  

Two things grab my attention here.  Sounds like you're using a Lee disk.  Nothing wrong with that, I also use Unique in my 45 Colt loads, but if you are getting a range of 6 - 7.6 grains of powder, something is definately wrong somewhere.  I use the 0.88 cc disk and it drops 6.8 grains of Unique, less than what the guidebook says.  Different lots will vary, but not by much.  I consistently throw within 0.1 grain with mine and others I've checked.  The other thing that could potentially cause problems is if you try these very light loads with jacketed bullets.  The jacket may stay in the barrel and the lead portion may go downrange.