OAL for a CPX 2 9mm

[LeftyTSGC]

I am doing reloads for target practice for my SCCY CPX 2 9mm.

I have chosen a OAL of 1.110 based on doing a Plunk test and backing off .020

From case mouth to lands is .103 (using a black marker on bullet)
The plunk test shows the ogive hitting lands a approximated OAL of 1.136, then I reduce by .020 (just a habit choice of reduction that seems to give best accuracy) this gives 1.116 so I rounded down to 1.110.

My concern and question is what do you set your OAL for your CPX 2, I am asking since the ramp on barrel is real steep compared to my other handguns. When I racked a few shells with only bullet and brass to find OAL at certain lengths the bullets would be slightly set back.

What affects the feeding more on a steep ramp, a short or long OAL?

I am using 124gr Xtreme HP bullets.

 

[gamestalker]

I have CPX1's, but I think they have similar ramp profiles. I'll look in my log books in the morning and get back to you with that oal.

But as far as oal is concerned and set back, when using the longest oal that fits the magazine / barrel, I've not experienced any set back issues. It actually kind of sounds like more of a neck tension problem, rather than a ramp / oal issue? Try taking a loaded round and pushing it against your bench, measure before and after to see if it set back, it shouldn't. And another consideration is, it isn't recommended to rack them more than necessary to check function / feed, as this can cause set back when repeated multiple times.

Also, check the ramp for burrs and rough spots that could be causing unnecessary friction against the bullet as it slides up the ramp, and can cause it to jump up into the hood.

GS

 

[tyeo098]

My standard 1.159" in Berrys Plated 124 RN's never caused any issues with my CPX-2

If you get setback you dont have enough tension. Taper crimp or expand the mouth less.

 

[LeftyTSGC]

WoW 1.159 where does your bullet hit the lands? Mine hit a 1.136 so I used that to set the OAL to 1.110.

I figured out why I had the setback, I kept using the same piece of brass and bullet, used a kinetic puller and pushed the bullet in by hand. After about 4 times i guess it looses tension.

Do any of you notice your ejected shells going all over? Mine will extract anywhere from my 1oclock to my 6 Oclcock from three to 10 feet. No common point anywhere.

That is what got me worried about my OAL, i wanted to make sure that i am not making hot loads. My current loads are 124gr Xtreme 9mm HP 4.3gr W231 set at 1.100. I have not had a chance to Chronograph anything, I am hoping for this weekend.

 

[tyeo098]

The only time I had a problem with hitting the lands was with my Lead 105gr SWC bullets.
Never had that problem with RNs...?

 

[jcwit]

The overall length that I load my 9mm for both my SCCY CPX1 & CPX2 is 1.1135. This is using Berry plated bullets in 100 gr., 115 gr., and 124 gr. Also 100 gr. X-Treme bullets.

In reality overall length is also dependent on the shape/radius of the bullet you are using.

I have no feeding problems what so ever. In fact I have no problems with my SCCY guns at all.

 

[LeftyTSGC]

Thanks for all of the comments on OAL.

What about the shell extractions? Are any of you seeing the shells going in all directions and distances?

I will head out this weekend and Chrono my reloads with various powder loads set at 1.110 OAL and see how they perform.

 

[gamestalker]

No, actually they eject quite consistently and predictably regarding distance and local. But, I also only load jacketed bullets and only load full throttle loads with Longshot, so my brass flies into the next county, but consistently.

BTW, I really like both mine and my Wife's CPX-1's, super good firearms for the money.

Considering you've identified and corrected the set back issue, I'm speculating that one, or a combination of the following may be causing the radical ejection trends.

Are you possibly using SPM primers? that might create erratic pressures, thus erratic ejection.

Xtreme HP's are a thick plated bullet, which is recommended to be loaded around mid jacketed tables. This would mean about 4.6 grs. would be about mid table according to Hodgdon for those 124's. To low of pressure could result in poor or inconsistent sealing as the bullet enters the barrel when fired. Maybe this is causing erratic extractions due to erratic pressures.

What do the fired cases look like, any dings or dents to indicate they are hitting or getting deflected off of the ejection port?

As for oal and feeding, a longer oal will feed smoother, thus reducing bullet deformation and set back due to blunt nose impacts.

Something you might want to try that has worked perfect for me since the 40 cal. came into production. I completely stopped belling and crimping the case mouths. Instead, I chamfer the inside of the mouth enough to create a nice beveled surface for the bullet to seat straight and smooth into. What this has done for me is, I am able to consistently attain maximum obtainable neck tension, and consistent neck tension, which entirely eliminated occasional set back 100%. And I also don't have to deal with some brass getting belled or crimped more or less than others due to variations in brass lengths, which causes sporadic set back. So for those that don't maintain / trim their AL brass to same lengths, this is a sure fire way to get consistent and maximum neck tension. This could be especially useful when loading for a firearm with a steep feeding ramp, such as the SCCY's.

Other than the above speculations, I don't have a definite solution to offer. Maybe try a slower burning powder like HS6 or Longshot, couldn't hurt, well other than recoil to the wrist and hand that is. For your CCW carry loads, you can't get much better velocity and accuracy than with Longshot. But don't expect to get decent results at the lower end of the tables, it need full operating pressures to function well, therefore recoil will be quite noticeable.

The data you posted demonstrates the nature of oal sensitivity in the 9mm. I really liked the way you logged the results of your loads, it really portrays those effects and characteristic regarding oal and velocities. Also great to have for future loads, provides a good baseline.

Hope this helped more than confusing things? I tend to get carried away sometimes.

GS

 

[LeftyTSGC]

Gamestalker, thanks for all the comments. Yes my brass is marked and dinged on some when ejected. When I emailed SCCY they said " that is normal for the CPS series, and happens on a lot of compact handguns.

I am using standard primers, WSP. I may eventually set the OAL longer as I keep trying new rounds. I barely have a bell on my shells, basically none at all, so I do not need to worry about the crimp.

I went back out today and Chronographed a few rounds, see attached, I compared them to my STAR 30M which is a full size all steel handgun.

Compared to previous times I used the Chronograph I noticed that for the same bullet, that Cold weather has a different effect on the rounds than does hot weather. If I can ever find powder other than W231, I will try it with my GDHP bullets.