Ruger MPR need AR Experts Advice

[Deleted member 48126]

I need advice on a Ruger MPR. I keep reading posts about the AR556 and MPR about hit or miss assembly, components, reliability... I have it listed for trade right now in the classifieds, but I doubt anyone will want to trade.

This was supposed to be a home defense / SHTF rifle / range toy / training rifle. It has 60 rounds down the tube. Its actually really accurate. I am getting a about 1.75 to 2 MOA with 55 grain FMJs and then it gets around .9 MOA with 69-77 grain SMKs for 5 shot groups off caldwell sand bags. The one issue that I am already having is failure for bolt hold open on the last round. Which is kind of discerning.

So here's the advice I need. Do you gents have a list of things I need to check specs and parts I should go ahead and replace? Does anyone know torque specs on ARs? Best practices / standards for building ARs? Any special tools I may need? Like if the barrel nut is over torqued (common issue with these rifles) as an example. I guess what I'm asking is what's the best approach to go through this rifle with a fine tooth comb? Thanks, any and all advice is appreciated.

 

[Another Casual]

Run the gun and stop reading what other people think about it. In a few thousand rounds you'll get a good idea of if its reliable or not. By that point you'll be well versed with it and you'll know if its the right tool for the job.

 

[Deleted member 48126]

Run the gun and stop reading what other people think about it. In a few thousand rounds you'll get a good idea of if its reliable or not. By that point you'll be well versed with it and you'll know if its the right tool for the job.

Do you know about the bolt hold open issue on last round fired? I feel like that's an easy fix, just not sure what causes it. Thanks for the reply.

 

[asd9055]

Do you know about the bolt hold open issue on last round fired? I feel like that's an easy fix, just not sure what causes it. Thanks for the reply.

Have you tried with different make magazines? In my mind it is either the magazine or the bold release catch/lever
I am not a gunsmith, hope one will chime in
FYI my Ruger MKII pistol will fail to stay open when it is dirty

 

[Andrew Massi]

Do you know about the bolt hold open issue on last round fired? I feel like that's an easy fix, just not sure what causes it. Thanks for the reply.

Its either the bolt catch or the follower on the magazine.

 

[Deleted member 48126]

Have you tried with different make magazines? In my mind it is either the magazine or the bold release catch/lever
I am not a gunsmith, hope one will chime in
FYI my Ruger MKII pistol will fail to stay open when it is dirty

Yeah, I have several. Standard Mil spec, magpul gen II & III, mission first tactical and then 30, 20, and 10 rounder models in the magpul and MFTs.

 

[Deleted member 48126]

Its either the bolt catch or the follower on the magazine.

Duh...I am dumb. Thank you.

 

[Deleted member 119066]

Few questions.

does it sometimes lock back?

If you insert an empty mag and then charge yourself does it lock back on the empty mag?

does it happen with all types of ammo or just some?

what bugger weight is in it?

My initial thoughts are it's either over or under gassed with a maybe that the bolt catch itself is imperfect. Ruger is usually great with this stuff so you could always RMA it

 

[cohunt]

As post 8 states. It could be a gas issue.

Load 1 round in your mag, close bolt- fire-- now 3 questions
1st question- does bolt lock back fully?
2nd question- where did the brass land in the ground ( use the "clock hand position" to describe which direction and also approximate how far - in feet- from you it landed)
3rd question- are you using factory ammo or handloads to test function?

Could be a mag issue, could be a bolt catch issue, could be under gassed ( too small of a gas port), could be over gassed with a bit of bolt bounce, could be an ammo problem-- your answers to the 3 questions above will help narrow things down.

What magazine are you using? Have you tried a different brand magazine?

 

[cohunt]

Are you running the mid length gas/16" barrel or the rifle length gas/18" barrel?

I'm assuming everything is factory/stock?

I've read some people had issues with things being loose on these, quite a few had handguatds come loose and initially the set screws on the gas block were comming loose and the gas block was moving ( making it under gassed)

It can be fixed, just a bit of troubleshooting-- change 1 thing at a time to see what fixes your issue.

 

[Deleted member 48126]

@cohunt @stretchr thanks for the replies. So, before I answer these, I just ended up selling the MPR and bought a BCM Recce 16. Blasphamy, I know not trying to solve my issues, but with my job and all the traveling I do, I didnt want to mess with it and order parts. So, in the spirit of the thread, maybe this will help someone out who is having issues with the ruger AR556 / MPR.

1st question- does bolt lock back fully? No it does not. Similar function to an AK. Last round failure to hold open and you squeeze the trigger thinking you have another round chambered.

2nd question- where did the brass land in the ground ( use the "clock hand position" to describe which direction and also approximate how far - in feet- from you it landed) I think the 5 o'clock position. I remember picking up my brass two benches over and behind me.

3rd question- are you using factory ammo or handloads to test function? Only factory ammo. 55 Grain FMJ of PMC Bronze, American Eagle 55 grain FMJ, 75 grain Hornady Frontier Ammo, and then the white box Hornady 75 grain ELDM.

 

[cohunt]

5 oclock-- it's probably under gassed.

I know you sold it, but 1st step would be to check the gas block and hole, if they are unobstructed and positioned correctly and tight, then the gas hole would need to be enlargerd by 1 drill bit size then re-test

Brass should extract about 3-4 o clock, 5-6 is under gassed-- 1-2 is over gassed

 

[Deleted member 119066]

undergassed

if it had a heavy buffer a carbine buffer would be in order. If it's a carbine you have to Hope the gas block is in a little wonky but I bet it's an undersized port and with the rifle gas of the mpr there's just not a lot of excess to help you. The world is enamored with reducing recoil through gas reduction now sometimes it's nice to have a little extra….

good swap, you got a great rifle