9mm Pistol Chamber Variation and Its Effect on OAL

[Gnnut2]

I am new to the forum and I must say that I find it very informative and thought provoking. I'm boning up on my reloading skills and I have realized some short comings with my pistol reloading techniques. I did not think about using the plunk test until I had problems with some cycling issues using RMR JHP 115 gr. bullets in my 9mm pistols. I realized that the OAL was excessive for proper chambering. I found a thread here that discussed the need for a relatively short OAL for these bullets. I am developing a plunk test chart for each 9mm pistol I own for these bullets. I have some 115 gr. and some 124 gr. I look forward to finding out how much variation from pistol to pistol there will be. I realize that all chambers are supposed to be cut and reamed according to the SAAMI specs, but given the myriad of bullets available today OAL can vary a lot. If anyone has any thoughts they would like share please do.

Regards,
Gnnut2

[George16]

I highly recommend you to read the links in this sticky:

https://czfirearms.us/index.php?topic=100352.0

[Gnnut2]

George16,

I have been reading those articles and they are very helpful. I appreciate your suggestion.

Gnnut2

[Wobbly]

All gun chambers sold in the USA need to meet SAAMI specs. But SAAMI doesn't define every last dimension within the chamber area, and specifically "freebore" (the un-rifled part of the barrel) is the one that concerns us most. So each gun maker decides how they want to dimension that part of the barrel to meet their needs.


Fig A

If you own several different brands of 9mm pistols, then on the first several bullets you reload you'll be required to remove all the barrels and do or little "pushing test" as explained in the "Stickies". You'll probably find in very short order that all your CZ and your Springfield striker guns take an exceptionally short OAL. So what I advise is that you reload ALL your 9mm ammo for those pistols, and then the same ammo will also work in your Rugers and Glocks equally well. In other words, manufacture to the most stringent requirements and the same ammo can be used in those pistols with more spacious chambers just fine.

So you don't need a chart, you simply need to locate the "tightest" chamber in your collection.

Now, be aware that bullets can foul the chamber/rifling 2 ways, so the tightest chamber may not always be the CZ... depending upon the shape of the ogive. Here's a cartoon that tries to show what can happen, with the "desirable situation" being in the center example...


Fig B

But note that RN gives the least "trouble" while the fancy shapes (generally only for sale in the USA) can cause the most grief.


Hope this helps.

[Gnnut2]

I read your sticky on this subject and immediately put my plan in place to have a designated small notebook for each pistol using a range of bullets. I actually did the work last night for several of my 9's and reviewed my data this morning. I immediately noticed that I can tweak the OAL just a smidge and get all but one pistol to function properly with the RMR bullets. I drew a diagram illustrating a loaded round using an average case length and on the actual bullet dimensions. From these references I calculated the seating depth, bullet projection above the case mouth, and the vertical distance for the propellant. It's interesting to note the latitude that a generous chamber offers, but on the other hand you don't have the bearing surface for the base of the bullet that a shorter chamber offers.

Thanks,
Gnnut2

[George16]

What other pistols (aside from your CZ) and powders are going to use these bullets with?

 I had used 124 Gr RMR JHP and due to the profile or bluntness of the ogive, I load it to an OAL of 1.102 for my shadow 2  with 4 Gr of sport pistol. I also used these reloads on my X5, TSO and MPX even though these other guns can accommodate longer OAL. Since it’s accurate for action shooting , I don’t want to waste my time loading different OAL for each specific 9mm gun I have.

By the way, I have never trimmed 9mm cases since I started reloading. There’s no need for it. I do however, trimmed rifle or bottleneck cases.

What shooting discipline are you using these bullets for?

[Wobbly]

I immediately noticed that I can tweak the OAL just a smidge and get all but one pistol to function properly with the RMR bullets.

Time to start dealing in absolutes, not general info. Please name those barrel makers.

I drew a diagram illustrating a loaded round using an average case length and on the actual bullet dimensions. From these references I calculated the seating depth, bullet projection above the case mouth, and the vertical distance for the propellant.

• Those are good steps. Of all the concerns, the height of the powder matters the least. Nice to know, but very few powders really care about "compressed loads".

• You also need to calculate in some excess to cover your own cartridge variations due to the fact that as a novice reloader, YOU will introduce OAL variations. Very few novice reloaders can hold an OAL goal to +/-0.002", it's going to be more like +/-0.010". This comes under the heading "Poop Happens".   

It's interesting to note the latitude that a generous chamber offers, but on the other hand you don't have the bearing surface for the base of the bullet that a shorter chamber offers.

• Generous chambers allow you to use strange shaped bullets, and that's about it. The blunt nosed RMR bullets being a prime example. Their RN and JHP are great bullets, but not a strong choice for the CZ (as much as I hate to say this because as a company, I really like RMR).

• The 9mm Luger cartridge likes its bullet seated fairly deeply, so in generously proportioned chambers this "space" is usually wasted, in that the maker is giving up some accuracy. To get that free accuracy, you'll most likely be seating deeply regardless of what the chamber allows. So loading for the CZ is actually a stronger position, when you own multiple brands.

• The handgun with the most generous chamber (Glock) is after something different. They are the number one seller to police forces, and so their sales pitch is "fires every time no matter what". LEO personnel are primarily concerned with answering an armed response. Their gun must fire, even if you just picked up a mag from a mud puddle. So they are following a completely different set of requirements. And it's an absolutely fantastic gun for those requirements. But those are not the requirements of most civilians.


Hope this helps.

[Gnnut2]

What other pistols (aside from your CZ) and powders are going to use these bullets with?


What shooting discipline are you using these bullets for?

I have three CZ pistols, one each by Sig, FEG (S&W 59 Clone P9RK), Browning, Kel Tec, So far I have used these bullets in the CZ 75BD, and the Kel Tec P11. After adjusting the seating depth the 75 ran them okay. The Kel Tec didn't object to the longer OAL. I will be trying them in the others.

I have used 5.3 grains of WSF in one load and W231 in the other. I do not remember the exact load, but I'm thinking around 4.l grains.



I'm only a recreational shooter and I don't compete. I do love to shoot and smell the powder burn, however.

[Wobbly]

I did not think about using the plunk test until I had problems with some cycling issues using RMR JHP 115 gr. bullets in my 9mm pistols. I realized that the OAL was excessive for proper chambering.

• The RMR JHP is a rather blunt nose bullet, and more closely fits the cartoon figure on the RH side in the second diagram, which is labeled "Fig B".

Following the instructions in the Stickies for the "push test", most people end up using an OAL around 1.060" for both the RMR RN and JHP when using this bullet in any CZ. This is an extremely short, but workable OAL. No feeding issues have been reported to date with this bullet/OAL combination. In fact, I use the 124gr version myself. Compare that OAL number to what you're using, please.

If you are happy with the performance of the RMR, then by all means keep using it. Some people consider that the short OAL takes it out of the "optimal" category when it comes to bullet purchase time, and prefer a bullet that uses a slightly longer OAL. This falls into the "peace of mind" category since no faults have been reported with the RMR bullets in CZs. But on your next purchase, you might investigate the Precision Delta JHP and the product from Zero bullet company. These both seat at 1.100" and are slightly cheaper in volumes of 3000.

Additionally, the CZ barrel seems to be designed around the 124gr bullet. By using the middle weight bullet, a lot of the "snappiness" comes out. So you'll probably enjoy your target sessions a lot more with the heavier bullet. 115gr shoots faster, and therefore flatter over distance. Some of your choice will depend upon your target distance.


• Can't comment on the WSF because I don't shoot a lot of 115gr bullets. In reviewing all our WSF testing, we simply had no testing at that weight. Would love for you to contribute your chrono info if you have any incremental load info you can share.

Hope this helps.

[George16]

What other pistols (aside from your CZ) and powders are going to use these bullets with?


What shooting discipline are you using these bullets for?

I have three CZ pistols, one each by Sig, FEG (S&W 59 Clone P9RK), Browning, Kel Tec, So far I have used these bullets in the CZ 75BD, and the Kel Tec P11. After adjusting the seating depth the 75 ran them okay. The Kel Tec didn't object to the longer OAL. I will be trying them in the others.

I have used 5.3 grains of WSF in one load and W231 in the other. I do not remember the exact load, but I'm thinking around 4.l grains.



I'm only a recreational shooter and I don't compete. I do love to shoot and smell the powder burn, however.

4.0-4.1 Gr of Winchester 231 is what I used to load those RMR 124 Gr bullets (including PD JHP ) before I shifted to using Alliant’s Sport Pistol.

Now, I m using Precision Delta’s 124 JHP, I load them up with 4.0 Gr sport pistol at 1,120-1.125” for use on my shadow 2, TSO, Sig X5 and MPX. Same load for all and works well. The Precision Delta JHP were also cheaper compared to the RMR JHP since I bought two cases of 3600 during their Black Friday sale since I compete and shoot a lot.

Good luck.

[Gnnut2]

4.0-4.1 Gr of Winchester 231 is what I used to load those RMR 124 Gr bullets (including PD JHP ) before I shifted to using Alliant’s Sport Pistol.

Now, I m using Precision Delta’s 124 JHP, I load them up with 4.0 Gr sport pistol at 1.120-1.125” for use on my shadow 2, TSO, Sig X5 and MPX. Same load for all and works well. The Precision Delta JHP were also cheaper compared to the RMR JHP since I bought two cases of 3600 during their Black Friday sale since I compete and shoot a lot.

Good luck.

George, I obviously posted your quote without a response. Wrong button! However, I do appreciate you sharing your experiences with me. I will check out the PD bullets as you and Wobbly have suggested and I look at Alliant's SP powder. I have many several powders made by them. I hope to improve my shooting skills and I would really like to short accurately and fast as you competitors do. It'll take lots of practice, but I'm improving.

[Gnnut2]

I did not think about using the plunk test until I had problems with some cycling issues using RMR JHP 115 gr. bullets in my 9mm pistols. I realized that the OAL was excessive for proper chambering.

• The RMR JHP is a rather blunt nose bullet, and more closely fits the cartoon figure on the RH side in the second diagram, which is labeled "Fig B".

Following the instructions in the Stickies for the "push test", most people end up using an OAL around 1.060" for both the RMR RN and JHP when using this bullet in any CZ. This is an extremely short, but workable OAL. No feeding issues have been reported to date with this bullet/OAL combination. In fact, I use the 124gr version myself. Compare that OAL number to what you're using, please.

If you are happy with the performance of the RMR, then by all means keep using it. Some people consider that the short OAL takes it out of the "optimal" category when it comes to bullet purchase time, and prefer a bullet that uses a slightly longer OAL. This falls into the "peace of mind" category since no faults have been reported with the RMR bullets in CZs. But on your next purchase, you might investigate the Precision Delta JHP and the product from Zero bullet company. These both seat at 1.100" and are slightly cheaper in volumes of 3000.

Additionally, the CZ barrel seems to be designed around the 124gr bullet. By using the middle weight bullet, a lot of the "snappiness" comes out. So you'll probably enjoy your target sessions a lot more with the heavier bullet. 115gr shoots faster, and therefore flatter over distance. Some of your choice will depend upon your target distance.


• Can't comment on the WSF because I don't shoot a lot of 115gr bullets. In reviewing all our WSF testing, we simply had no testing at that weight. Would love for you to contribute your chrono info if you have any incremental load info you can share.
=
Hope this helps.

Great information as always, Wobbly. I will compare my data as you recommended. You also mentioned chronographs. I do not have one, but I have been doing a little research on purchasing an affordable model that's reliable. I have even looked at the Lidar system and some folks don't seem to like it. The old Ohler 35 was one that I passed on several years ago and I now regret it. Do you have any suggestions?

[Wobbly]

Now, I m using Precision Delta’s 124 JHP, I load them up with 4.0 Gr Sport Pistol at 1.120-1.125” for use on my Shadow 2, TSO, Sig X5 and MPX. Same load for all and works well.

George -
You might want to check that OAL. I'm not aware of anyone using the PD JHP bullet at any OAL longer than 1.110". For most people it's closer to 1.100".

 

[George16]

Now, I m using Precision Delta’s 124 JHP, I load them up with 4.0 Gr Sport Pistol at 1.120-1.125” for use on my Shadow 2, TSO, Sig X5 and MPX. Same load for all and works well.

George -
You might want to check that OAL. I'm not aware of anyone using the PD JHP bullet at any OAL longer than 1.110". For most people it's closer to 1.100".

 

Wobbly, I was very surprised myself when it passed the plunk test on my shadow 2 chamber at that OAL. I had to use the shadow 2 for plunk testing  since it has the shortest chamber among my pistols plus the 2 MPX (gen 2 & 3). Somehow, it did and I was so happy about it. Now, I only have to use one set of powder, bullets and die set to load for all of my 9mm guns.

That’s the main reason I bought a lot of those PD JHP during their Black Friday sale. It’ll tide me over until their 4th of July sale  . I also sold my remaining 8 lbs of Winchester 231 and RMR JHP to a friend to buy more sport pistol and primers  .

By the way, my shadow 2 barrel is stock and not reamed.

[Gnnut2]

I did not think about using the plunk test until I had problems with some cycling issues using RMR JHP 115 gr. bullets in my 9mm pistols. I realized that the OAL was excessive for proper chambering.

Following the instructions in the Stickies for the "push test", most people end up using an OAL around 1.060" for both the RMR RN and JHP when using this bullet in any CZ. This is an extremely short, but workable OAL. No feeding issues have been reported to date with this bullet/OAL combination. In fact, I use the 124gr version myself. Compare that OAL number to what you're using, please.

Wobbly, here are my push test results for the RMR 115 and 124 jhp bullets:

The 75BD and the SP-01 averaged the same for each bullet. 115 OAL = 1.084, 124 OAL = 1.060 ( just as you said). My loaded ammo will be 0.015 shorter than these numbers for a safety factor.

The Rami, however, was a little different. 115 OAL = 1.086, 124 OAL = 1.062. I'll load all three of these pistols the same. They are definitely siblings..