A bit of info first...

I'm loading subs for a Sig MPX which has a AR styled trigger that can only be described as garbage.  It currently breaks at a massive 10lb average!  

With a bit of polishing, the gritty feeling is almost gone but the overall performance would be greatly enhanced with a much lower pull weight.  Enter the JP reduced power spring kit.

Since this spring kit is designed for a typical mil spec AR FCG, it can be installed in the MPX with no issues.  Here's the catch...

In some AR's (.223/5.56) using NATO ammo or other ammo with harder cupped primers, this spring kit seems to be unreliable with many FTF's reported. IE: light primers strikes.

Since the MPX is a 9mm, obviously using small pistol primers, how do these primers compare to small rifle primers?

As close to apples to apples...  How do you think a typical CCI small pistol primer (No. 500) would compare in cup hardness to a typical CCI small rifle primer (No.400)?

I think you will be fine.

I have a 22 tcm rifle that will not consistently ignite small rifle primers, but it has no issues with Small pistol primers. They are much softer so as to be able to be lit off by striker fired hand guns.

I use cci 500s in my 22 tcm now, I tried cci #41s (90% failure to ignite), cci400s(50% failure rate), s&b srp (40% failure rate).

Many thanks for the response!



I decided to just go ahead and order a spring set.  It's a $20 experiment and a bit of time on the 550, so what the heck...

If it doesn't work, it wouldn't be the first time I retired parts to the "spares" drawer...  LOL!!

I'm duplicating a 147gr. recipe that works fine through my suppressed HK P30L so it's a "win" on the ammo side even if the springs fail.

On a side note...  Merry Christmas and Happy Holidays to you and "TheUnicorn"...  

I think you will find that there is no difference in hardness, but there is a difference in thickness.
Right or wrong?

With CCIs, it's not so much thicker/harder as "tougher," I think.  There is evidence that CCI's small rifle and small pistol primers use slightly different cups, but that's not something CCI is going to in any way clarify for us.  Trade secrets and that sort of thing...

Moose, you may have success with the JP springs.  I'd go a step farther than the polishing you've done.  Clean the trigger and hammer pin bores, then add a light grease inside them.  It's given me measurable improvements in stock AR FCGs.

Yes pistol primers are thinner than rifle primers. OP I think you will be ok.

If you truly have the trigger & hammer cleaned up on an AR type trigger you can probably use a full power hammer spring, and a reduced power trigger return spring. The difference with the heavier hammer spring and good lubrication should be negligible if you got the trigger right.

Agreed!  

With both reduced power springs AND a disconnect spring, add in the current parts, I'll have quite a few options to play with if light strikes show up.

The CCI 450 and #41 are the same small rifle magnum primer with the difference being anvil placement and price. The 400 small rifle standard is thinner cup (results in being 'softer') and less 'flame'. The CCI 550 Small pistol magnum primer is for all intents and purposes identical to the CCI 400 Small rifle primer. I use them interchangeably, get same accuracy and velocities in same loads. In general, I've found CCI primers to be among the 'harder' primers, and Federal to be among the softest. Had to use Federal with light hammer spring in GP100, just not enough force to reliably ignite CCI 550 magnum primer.

May be just me but: There is a member that sales the Rock River NM standard and Varmint triggers on the EE for around $86 shipped. This seems like a lot less work plus you end up with what's in my humble opinion the best trigger for dollar spent in the AR world.

Motor