40 S&W Bullet Tension and Setback

[Bret]

tdogg, is that Glocked case one that you fired through your pistol and recovered or is it just one you found at the range?  The reason I ask is that I'm perplexed by the bulge.  I've shot a ton of 40S&W cartridges through my Gen3 Glock 23 and have never once had a bulged case.

[IDescribe]

I have the same question.  That doesn't look like a Glock bulge to my eye.

[tdogg]

No those I pick up at the range and are left over from law enforcement.  I couldn't tell you what brand firearm they use?  I will say that most of that brass (it's all Speer cases) has this slight bulge near the extractor groove.  It is small but noticable.

Upon close inspection, it isn't symmetric around the case.  Typically one side has more bulge than the other.  My pictures don't really show the bulge well.

I don't own a Glock and I never have.  I use the term glocked based on internet folk lore with 40S&W.  From what I've read, the Gen 1 and 2 models were the reason for the term.

Any manufacturer with a loose chamber shooting upper end loads could cause this slight bulge.

Cheers,
Toby

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[Wobbly]

This is "Glock bulge"...

[Bret]

Combine that with setback and it's fun times at the range.

[tdogg]

That Glock bulge is extreme!  I think these bulged cases are from a loose chamber not a partially unsupported chamber as with the Glocks.  The bulge has a smooth transition all the way around.  I don't think I'd trust/use a true glocked case in my loads!

The small base die does size farther down the case closer to the extractor groove.  You can kind of see it in the pictures posted above.

Thread drift!

I'm going to work up a new ladder load today.  Probably going to have to reduce the load a little too make the same power factor with the increased bullet tension/reduced case volume. It will be interesting to see by how much.

Cheers,
Toby

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[tdogg]

Got out and shot my new ladder load today with the EGW sizing die.  It was a little chilly but sunny and fairly calm.  I shot all these at 10 yds off a rest and did try to shoot them accurately.



I saw the power factor drop about 2 (velocity dropped ~10 fps) from the last time I ran a ladder load.  It was about 20 degrees colder this time around...

I saw about the same accuracy at the same velocities from before the charge that showed the best accuracy was a little higher (given the velocity drop due to temp).  I didn't see any efficiency gain from the higher bullet tension.



The four groups from the ladder (4.4-5.0) start at the bottom left and go clockwise around the target.  Take note of the middle group, that is my Gold Dot SD load and is a 10 shot group pushing 165gr Gold Dot ~1160 fps (192 PF) out of my TSO!  Stellar group!



Same as above just a replicate set of groups.  The center group is the same Gold Dot load shot out of my newly acquired 40 upper mated to my SP01 tactical frame (can swap it out for the stock 9mm slide).  It was only pushing the gold dots ~1110 fps (184 PF).  Also a stellar group!

It is interesting that the 5.0 groups are so poor compared to the 4.8 groups.  It's unfortunate as I really should be running about 170 PF for USPSA.  Since I shoot mostly at my local club I choose to shoot the 4.8 load as it is much more accurate (I repeated this several times now and it doesn't appear to be a fluke).  It's just barely over the minimum power factor but we don't ever chrono loads at my club.  As the temps climb it will increase and give me a little bigger buffer.

Bottom line I don't have to alter my charge given the increased bullet tension of the EGW sizing die.  I was sure I would gain some efficiency but the chrono doesn't lie!  These cartridges don't setback with the EGW die, problem solved!

Cheers,
Toby

[Wobbly]

Interesting.

[Bret]

I'd definitely stick with the 4.8 load.

[IDescribe]

The primer creates enough pressure to open the case and release the bullet.  I wouldn't expect sizing a case slightly smaller to have much effect on how the powder burns.


As to accuracy, good for you with the 4.8 load.  I would suggest that it may not be simply the amount of powder, but the velocity at which the bullet is leaving the barrel.  As weather gets warmer, you may find you have some extra PF cushion, but you may also find that the extra velocity degrades accuracy.  You might find you need to drop to 4.7 as it warms up to maintain the same accuracy.    You may also find that that 4.9 is good to go right now.  Or 4.7 with slightly reduced OAL.  I would suggest that your current load at 4.8 is certainly in the Goldilocks zone, but you might find some additional tuning in that zone to be a good thing, and you might find that as it warms up, you might need to play around to stay in that zone. 

[Wobbly]

Got out and shot my new ladder today....

If I could afford a new ladder, my wife might have me up on the roof. That would be a good reason to shoot the ladder.

 

[tdogg]

Why do you think I shot it?  I'd be up there painting all the trim!

Wobbly...