10 replies to this topic

[SyberShooter]

I haven't been able to find the answer to the following question searching, so maybe some of you can help me out. If I haven't posted this question to the right forum, go ahead and move it.
Also, before I get started, I am experienced enough to know to work up my own loads from reduced starting charges, chronograph and to look for pressure clues as I go. So, to save some time we don't need to cover that again.

OK here are the background conditions,
When looking to work up a new load, we often search for posts using the desired powder & bullet or we ask for recommendations from others. Load data is abundant on various forums and often is accompanied with OAL and chrono data as well, so far so good.

(irrelevant stuff removed for brevity...al)

Recently I was doing some load research and happened to be looking at one of the "Jeff Maass IPSC Load Lists". As I was browsing I noticed that a lot of the notes indicated the number of ports in the source's compensator or that their barrel was ported. Some of these loads definitely looked high pressure to me, but I realized they needed the gas to work the comp.

Then it occurred to me - what would happen if it WASN'T mentioned that there was a X-port comp attached to this gun? Would that load blow up my uncompensated gun? Even if I reduced it 10% to start? What about the loads I collect from forum posts.... they don't always mention if they are running a comp or not, just that their load works great for them. Lots of what-if's go from there...

I do not have a compensator on my gun and during load development, want to be careful even with reduced starting loads ... if a load is higher than normal to work a comp, the typical 10% reduction for a starting load will also be higher than normal.

Now my questions... awkwardly worded as they are... redundantly asked in different ways. I'm not asking for details of comp. design, as I do know that will make a difference in the final answer, but a rule of thumb would be a good thing to know.

o- How many grains of powder should a comp load charge be reduced if no compensator is present?
o- How much extra pressure does it take to work a typical comp with X number of ports?
o- What affect does bullet weight have on this?
o- What is a typical range (in grains of fast/slow powder) OVER published Max, does the average compensator user load?
o- Do comps and ported barrels affect chamber pressure / max safe load in a similar manner?

Any added info along these lines would be appreciated. I am trying to come up with my own idea of a 'red flag' rule when I think a load is not quite right and that a comp might be used with a particular load recommendation.

Thanks
Al

Edited by SyberShooter, 03 August 2012 - 10:07 AM.

[Desmo412]

I believe that a compensator has no effect on the velocity or pressure of any given load when compared to a gun with an equal length barrel. Once the bullet enters the compensator, it is no longer accelerating. Barrel ports, on the other hand, bleed off pressure before the bullet has reached the end of the barrel. This will cause the need for more powder to make the same PF as an equivalent gun without barrel ports.

[Bamboo]

^^^^ what he said, plus each barrel has a personality all it's own - fast barrel, slow barrel, etc.

As an anecdotal data point, I have a 5" stock .45 and an old IPSC open .45 with a 5" barrel and compensator. I don't see significant differences is velocities using the same loads.

When working up loads, a chrono and the patients to build up loads slowly are your friends.

[superdude]

What Desmo412 is right on. Loads are not higher to work the compensator. They are higher to achieve a desired power factor. Slower burning powders, that require a larger charge weight, are the usual choice when using a compensator. More charge weight for the same velocity means more gas, and gas runs the compensator. Higher chamber pressure does not necessarily mean better compensator function. See the link below for information on pressure vs. gas.

http://38super.net/P...r Function.html

Many ISPC loads for 38 Super and 9mm Major are excess pressure because they are trying to reach a desired power factor with light weight bullets, and they often can't achieve that velocity and stay within SAAMI specs for that caliber (with their preferred powder). Excess pressure loads are only safe in guns with barrels that offer full case support. Without full case support there is a high chance of case rupture. See the link below for more information on this subject.

http://38super.net/Pages/Major.html

[SyberShooter]

Thanks for the replies and info, I feel a lot better about it now knowing the comp isn't going to affect pressure or velocity much at all. I was afraid the load data associated with comp guns might influence normal data in some way, skewing it higher.

My 38 Super and .40's all have full support and it was the loads for powders not found in most manuals that I was wondering about. I hear ya about loading to a PF, that's one reason I chrono my loads.


Those are GREAT links... thanks a lot!

Edited by SyberShooter, 03 August 2012 - 12:53 PM.

[Scootertheshooter]

I do believe that it affects velocity. I understand that different barrels have different results . I did shoot 2 different G34 with and without a comp just for the same question. One had a comp with a jagar barrel and another with a stock barrel . The stock was a 139 PF and the other with comp was at 131 PF with strings of 3 sets of 10. It only makes sense that if you put anything on the end of a gun barrel, comp, flash hider , brake or silencer with effect accuracy and or velocity to some extent.
The other question about powder charge and PF is kind of misleading . Shooters use more powder to make PF and to get the comp to work. I think it's unclear to say they use more powder only for PF. I could reach PF with a certain type of powder but need to increase the charge to produce more gas to utilize the comps performance .So sometes there is a need to increase a charge slickly to get the comp to work. JMHO

[superdude]

It's not valid to compare the velocity from two different barrels for this comparison. All you can say is that the two barrels have different velocity. You can't conclude anything about the effect of a compensator based on that. You have to do the comparison with the same barrel, with and without a compensator. No exceptions.

[Scootertheshooter]

It's not valid to compare the velocity from two different barrels for this comparison. All you can say is that the two barrels have different velocity. You can't conclude anything about the effect of a compensator based on that. You have to do the comparison with the same barrel, with and without a compensator. No exceptions.

True I do believe anything on the end of a barrel will affect its original function. Unless it was originally designed that way. Such as after market stuff.

[SyberShooter]

I think the point that I was looking for (and that I took away from above) is that the peak pressure at the chamber is going to be the same no matter if there is a comp installed or not. An unsafe over pressure load will be just as unsafe no matter what is hanging on the end of the barrel.

Did I interpret that correctly?

[superdude]

I think the point that I was looking for (and that I took away from above) is that the peak pressure at the chamber is going to be the same no matter if there is a comp installed or not. An unsafe over pressure load will be just as unsafe no matter what is hanging on the end of the barrel.

Did I interpret that correctly?

Correct.

[Scootertheshooter]

I think the point that I was looking for (and that I took away from above) is that the peak pressure at the chamber is going to be the same no matter if there is a comp installed or not. An unsafe over pressure load will be just as unsafe no matter what is hanging on the end of the barrel.

Did I interpret that correctly?

Correct.

I agree