Barrel length vs pressure

JWFilips

Well-Known Member
Hi Guys,
I had my wife out shooting ( it has been awhile) She shoots a 2" barreled Smith and Wesson Model 32 Terrier in 38 S&W.
She managed to go through 100 rounds since she wanted to make the most out of her too infrequent range sessions. So now I have to go back and reload for a pistol again ( think it has been 3 years) But I really don't mind the drudgery of doing them on my single stage rock chucker.

Her practice loads are mild however I noticed that the newest data shows the mild loads she is shooting look like near max pressure loads with a 4" barrel!
Huh? I know last time I loaded for her my data from multiple sources showed they were low to mid range in pressure for the little .38 S&W. Thats what I have in my notes.
One load in question is 3.2 grains BE with a 125 grain bullet. Why all of a sudden that should be considered a "hot" load?
Does the data for a 4" barrel increse preasure that much over a 2" snubby barrel?
 

Brad

Benevolent Overlord and site owner
Staff member
Barrel length should have little, if any, impact on pressure.
I bet what happened is a change in load data and testing. Older manuals were often guesstimated pressure. Now it is accurately measured. Much data from the 60s and 70s, and earlier, has been tamed down.
 

Brad

Benevolent Overlord and site owner
Staff member
Alliant still lists a 125 GDHP over 4.8 gr of BE as +P. I assume you are using a cast bullet and you are using far less powder so I think you are fine. The load listed on the Alliant site is a very significant increase over yours.
 

RBHarter

West Central AR
I know this probably doesn't need to be said here ........
The 38 S&W has 9 names and is chambered in 130+ old questionable guns . If the data hedges into 380 +P or 9mm start loads it's probably pretty close to max loads and not something you'd want in say a 1900 H&R top break or auto ejector .

Same deal we have with all those 93's for the 7×57 and 257 Roberts .......
 
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Ian

Notorious member
Similar trends with published data occur in many other cartridges, too. IDK but it smells like company lawyers justifying their existence to me. If it was just the antiques, well, weren't they around when the earlier data was published? Another theory is piezoelectric pressure data may have revealed anomalies which were invisible to copper-crushers, such as secondary spikes, and load data was altered to reflect this.

Another thing that most everyone knows but still bears repeating for fast powders in handgun calibers is case volume....or seating depth. A difference of only .020" in seating depth can put a mild load into +P territory or worse.
 

RBHarter

West Central AR
I wasn't thinking in terms of the antiques having already been proofed etc I was thinking about the powder changes and aging and the residual writings that say things like a half grain over under is ok etc . Can you get your head around a 2.3-2.7 load window and throwing 3.0 with a bullet that runs 5% heavy , with a hot lot of powder and a thick case , maybe throw in a few hot primers , a fat sprue and next thing you know your 14,000 psi load is pushing 23,000 and you have bolt divots in the chambers ..... It gets even more exciting with loose HS , tight cyl gaps , and on and on .

Speer #12 "why balastians get grey" ........ It's safe in mine use good judgement .
I'll go back to my box now .
 

fiver

Well-Known Member
the only part a barrel plays in pressure is in a closed system and then diameter and throat dimensions come into play.
length is more a function of muzzle pressure [which is important when shooting lead] but really has no bearing on maximum pressure.
 
F

freebullet

Guest
Looks like they answered your question. Good on you, JW, for getting the wife out to the range. Your not alone, mine tries to shoot up anything I bring too.
 
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JWFilips

Well-Known Member
I see good information here!
Always good to learn something that is why I ask questions on this forum!
Thank you
Jim
 

Pistolero

Well-Known Member
If the load has been comfortable, and you have loaded it before without drama, you can stick
with it. IME, and in published data, cast bullet of the same weight will result in higher
velocity and lower pressures than the equivalent jacketed bullet.

I have no fear of using cast in place of jacketed in published data, knowing my pressures
will be, at worst, the same, and almost certainly lower in reality due to lower bore
friction.

Tin-lead alloy against lubricated steel has about the lowest coefficient of friction known
for metals, which is why babbit metal was developed and is still used today, as the contact
surface on journal bearings such as auto engine main and rod bearings.

Most of the time a journal bearing is not in contact with the steel journal, being supported
on a film of oil with literally zero wear when running, but during startup, until the oil film
builds pressure and lifts the bearing off, our of contact, there is direct friction between
the babbit (tin-lead) and the steel with low friction coefficien, and therefore, long service
life. Our alloys have less tin than babbit, and our lubes are possibly less effective than
lots of motor oil at lower temperatures and pressures, but the situation is not entirely
different. We can expect low friction coefficients.

A fast powder like BE (or TG, Red Dot) will minimize muzzle blast, probably making a more pleasant
load than, for example 5.0 gr of Unique in a .38 Spl, a +P load. BUT - IME, even the slower Unique
loaded +P isn't particularly unpleasant from a snub nosed .38. If you wanted to change to a
slower powder like Unique, I doubt that the powder speed difference would cause much notice.

BUT - until you actually do it, all is just theory. My experience with snubbies is all with
.38 Spl, no .32 experience. So, it will have it's similarities, for sure, but it is not the same.

Bill