How much above groove size can you shoot in a .40 S&W?

[Greg G]

I have a new .40 mold that is dropping at .403". Can I shoot them "as - is" or Should I size them? It's a Glcok model 22 with a stock barrel. I also have a bar-sto barrel for it that is .400" groove diameter.

Thanks?

[DougGuy]

It doesn't matter about the groove diameter it matters about the throat diameter. Likely a .403" won't chamber but you can seat one and see if it will plunk. Some of the Glocks have some pretty generous freebore in the throat, so give it a try. Since the boolit also makes the shoulder of the loaded round larger, this can make it too big to chamber fully if the chamber itself is on the tight side, as in a match grade barrel where all the dimensions are minimal.

[Greg G]

It didn't chamber at first, so I made a tool to ream the cases to .401" only far back enough for the bullet to seat. (I'm a hard headed machinist).

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[tazman]

What DougGuy said is correct.
Basically the chamber/throat sets the limit. If it will chamber, it will shoot.
I have a Beretta 92FS that will chamber boolits sized .360, which really shouldn't be possible, but it does. And it shoots them just fine.
I have a Springfield Armory, Range Officer 9mm which has a much tighter chamber. It will only accept boolits up to .358, and those need to be perfect.
So I need to make sure of what ammunition I am using in the Range Officer since the Beretta will accept anything.
The same sort of thing applies to the 40 you have.
Chamber dimensions vary quite a bit from manufacturers. Experiment a bit. Let the gun tell you what it likes.

[Greg G]

What DougGuy said is correct.
Basically the chamber/throat sets the limit. If it will chamber, it will shoot.
I have a Beretta 92FS that will chamber boolits sized .360, which really shouldn't be possible, but it does. And it shoots them just fine.
I have a Springfield Armory, Range Officer 9mm which has a much tighter chamber. It will only accept boolits up to .358, and those need to be perfect.
So I need to make sure of what ammunition I am using in the Range Officer since the Beretta will accept anything.
The same sort of thing applies to the 40 you have.
Chamber dimensions vary quite a bit from manufacturers. Experiment a bit. Let the gun tell you what it likes.

Thanks guys for the advice. I was just worried if plus .003" over grove diameter would raise pressures too much and be unsafe. Thanks!

[Lloyd Smale]

Ive got a glock 23 40sw and two 10mm glocks a 20 and 29. None of them will run a 100percent with bullets any bigger then 401. you might get away with a mag full of them but eventually your going to have chambering problems. Especially after a couple hundred rounds of gunk gets built up in them.

[DougGuy]

Thanks guys for the advice. I was just worried if plus .003" over grove diameter would raise pressures too much and be unsafe. Thanks!

Any resistance will raise pressure, that's physics. I throat 40 barrels to .4025" for .402" boolits and it works out really good to size to .402" and have every round plunk. The longer throat reduces pressure, it lets more of the boolit into the freebore where it is centered with the bore much better than shorter throat or rifling that runs right down to the chamber mouth, it is as easy a transition from case to rifling as you can get. You are at this point pushing the limit of the stock barrel and throat with the boolit diameter. Going larger will only result in more interference. Have the barrel throated like the Glock 19 barrel in the photo, size to .402" and enjoy it!

http://i1202.photobucket.com/albums/bb374/DougGuy/Cylinder%20Services/Glock%20Throating/Glock19-640_zpsv5rzqop5.jpg (http://s1202.photobucket.com/user/DougGuy/media/Cylinder%20Services/Glock%20Throating/Glock19-640_zpsv5rzqop5.jpg.html)

[Greg G]

I rented a .402" throater a couple of months ago and did the Bar-Sto barrel I have.

[white eagle]

I be more worried about those cases you reamed

[DougGuy]

I rented a .402" throater a couple of months ago and did the Bar-Sto barrel I have.

The Bar Sto is a stainless barrel, they ream rather nicely. You won't have that kind of luck with the Glock barrel as it is salt bath hardened and it will RUIN a HSS reamer the first 1/4 turn you make with it. I had to have carbide reamers made to my specs to do hardened barrels, they are 3x and 4x the cost of HSS tooling, and their lifespan is less than a dozen barrels, afaik, mine is the only game out there for throating these hardened barrels. I don't know anyone else who has invested in carbide for throating.

[Greg G]

Well I shot 15 of these rounds, and I didn't see any pressure signs on the cases or primers. The .403" bullets didn't fix my leading problem, so I guess I'll load some gas checked bullets next to see. I have good fit, good lube, cases not sizing down the bullets. Hopefully the gas check fixes things.

Thanks guys.

[9.3X62AL]

IME, cast bullets at .401" have served me very well in CZ, Beretta, and S&W 40 S&W and 10mm barrels. All of these barrels and the chambers & throats are in OEM form. One of the nice things about the 40 S&W and 10mm barrels over the 9mm barrels is the absence of dimensional poetry of the 40/10 family.

Doug Guy--that barrel pic you show in Post #7 is my idea of a GREAT general-purpose autopistol throat/leade form. My own belief as far as the abrupt leade/short throat forms found in 40 S&W barrels is that it is form bias favoring and/or assuming the use of jacketed truncated-cone bullet forms in the factory ammo often carried in the 40 S&W pistols in service both publicly and privately. The form shown in your pic should accomodate a far wider range of bullet designs without interference.

Greg G--Some condition is allowing/causing propellant gases to get past the bullet sidewall--act as a "cutting torch" to the sidewall's bullet metal--and plate the bore with bullet alloy "spray" ahead of the bullet. The bullet's passage over that plating "irons" the plating onto the barrel surface. That is how barrel leading occurs, per the late Walt Melander of NEI Handtools. Resorting to a gas-check bullet design will not cause leading to actually stop occurring--you just won't see the plating because the gas-check scrapes most of the leading out after each shot's creation and removal of same. Accuracy still suffers, though leading "disappears".

My usual rule of thumb for selecting size diameter is at throat diameter to +.001". This applies to autopistols, rifles, and revolvers. In my sole case of a revolver built backwards (throats smaller than barrel grooves), I honed the throats to +.001" the barrel grooves, and size my bullets to +.001" the throat diameter. In effect, the Ruger Bisley 45 Colt now has .454" castings running through .453" throats and feeding into .452" grooves. Subtle funneling, for lack of a better descriptor.