Help. I'm stumped on a MPA switch lug

[bgavin]

I started having problems a couple months back. My MPA 6.5 creedmoor started shooting overpressure with Hornady eldm 140 grain. This was all of a sudden. This rifle had about 700 rounds of 140 eld without a hiccup. I never shot anything else the eld's shot so good. I had given the rifle a good cleaning so I thought it was something I did. I cleaned again and got heavy bolt lift and popped primers on the eld's again.

I called mpa and they said it was the ammo. I shot some more and same thing. This was from 4 different lots of eld's. I also tried sig 140 match and on the second shot the case got stuck. I sent it in at this point.

Al inspected it and said everything's good it's the ammo. I used a magnetospeed today and shot a few factory rounds and got 2868 for an average speed. No popped primers like last week but the primers are flat and looks like they were trying to come loose around the edges of each case. When the rifle had a couple hundred rounds on it I borrowed a magnetospeed and it was 2700 to 2720 flp with eld's. We also measured several other rifles with the same lot ammo today and 2 tikka's were around 2600 and a curtis axiom/bartlein was at 2710.

I got with a friend and loaded 140 eld h4350 40.1 up to 40.9 grains in .1 increments 5 shots each. We loaded at factory length. 40.0 grains were in the 2730's and I was at a little over 2800 at 41.9. This was with once fired hornady brass neck sized. All had flattened primers but no popped primers.

Any ideas whats going on? I want to start reloading but I also want to find out why I can't use factory ammo.

 

[abn31c]

I have the same rifle. 140 eldm goes 2775 with 41.7 gr. H4350, 130 berger hybrid goes 2885 with 42.1. Hornady brass on the eldm, lapua on the hybrid. Never fired a factory round.

 

[mustang-cars]

Check for a carbon buildup in the throat. Many will tell you that 6.5 CM won’t build a carbon ring but my experience has been quite the contrary. If you can get a bore scope to check the throat that would be ideal. Now I scrub my throat quite often. My first barrel I let the carbon ring get out of hand and it becomes very difficult to clean out.

 

[supercorndogs]

Carbon ring would be my number 1 suspect as well. It essentially shortens you throat to a condition where your bullets are jammed instead of jumping, thus raising pressure and velocity. There are a few thread about removing it.

 

[abn31c]

Since OP stated it happened all of a sudden carbon ring would be the #1 suspect. Ive been around around a couple of these barrels beside my own and I gather they make pressure/velocity with a lil less powder than most. OP I would start hand loading now and forget about factory ammo. If you walk around a match and look at most spent cases you can find signs of pressure on most, including factory ammo. Im not advocating high pressure, just passing along what I see.

 

[supercorndogs]

Lots of people push the ragged edge for no good reason.

 

[bgavin]

Yep I had a local smith check for a carbon ring and Al at MPA said everything was good with the barrel.

I’m going to call them again and try and send it back in tomorrow.

 

[bgavin]

Lots of people push the ragged edge for no good reason.

I don’t want to try for high speeds. I just want to find out why I can’t shoot factory eld’s anymore.

Got my friend to help reload some light loads to see if it was the factory ammo or the gun. Comparing speeds I’ve seen online somethings wrong with the rifle not the ammo.

 

[abn31c]

Out of curiosity, does the rifle have a excessive cold bore shot?

 

[bgavin]

I usually shoot at 700 first and true StrelokPro pro and first shot is about 3 inches left 4 inches high. The next two rounds walk in to my zero.

 

[abn31c]

Thats acceptable to me. Mine is 2 to 4 inches low at 100. I thought I had it fixed but it came right back. Mine does this on every string of fire, regardless of time in between.

 

[bgavin]

Thats acceptable to me. Mine is 2 to 4 inches low at 100. I thought I had it fixed but it came right back. Mine does this on every string of fire, regardless of time in between.

That’s odd it does it every string. Mine has been consistent high and to the left cold bore. Then stays consistent on 10 shot strings then I let it cool down.

I shot another 50 today my friend helped me reload and started at 38.5 and worked up to 39.4.

The velocities look better. The 38.5 was around 2665 and 38.5 was around 2700.

I’m still going to give MPA a call because I shot one round of federal non typical 140 grain I use in my tikka hunting and it was 2843 FPS. I want to be able to shoot factory ammo and even the federal is 100 FPS faster in my rifle than it should be.

 

[NamibHunter]

I have the same rifle, but it only arrived two days ago, and have not shot it yet as i have been out of town.

My initial checks have indicated that the MPA barrels are cut with fairly tight chambers. Not as undersized as BR tight neck chambers, but towards the lower end of the SAAMI spec. From what i have read and heard from comp shooters, i believe MPA’s intent is for factory ammo to have less slop in the chamber, and this helped amongst other things to enable them to provide the 3/8’th MOA guarantee (using Hornady ELD-M factory ammo) for 6 mm and 6.5 mm calibers. [Which is an impressive claim. Will test that soon.]

So on day one, i FL resized 5x fired Lapua brass with a Redding Type S die, and none of them would fit in the chamber, not even close. Bolt has 1/4” of travel left before it can even start to close. Case length (6.5CM) is below min at 1.905”, max spec is 1.920”, so case length is not the issue here. Resized cases fit neatly in my LE Wilson case gauge, so i don’t think the die is out of spec. This particular Redding die has worked fine for me on two prior barrels (stock Savage Model 12 and a Shilen Select Match), so i probably cannot blame the die.

Undersize chambers will of course give higher speed and produce overpressure earlier than the typical oversize chambers cranked out by factories like Remington, Ruger and Savage. The book data is based on test results with a factory barrel, for the most part.

You should have seen higher than published speeds from the start, and that can sometimes be ok for a while, until either ambient temp goes up (and the powder is a little temperature sensitive, and they all are to some degree, and mid summer has arrived), or a carbon ring becomes excessive enough to cause problems, and / or the throat gets rough from fire cracking and the bullet sticks for longer in the lands before it flies down the barrel. Could also be a combination of these factors. Also different lots of bullets can have a 20 or 25 thou difference in bullet base to ogive measurement, so a 5 thou jump can turn into a moderate jam by changing over to a different batch of bullets or factory ammo.

I watched a video where the owner of MPA talked about bullet seating and my impression was that they throat their rifles to have a 0.005” jump, for the factory Hornady ammo they cut the throat for. So the Hornady ammo might well have minimal jump, and is already very close to a jam. You will not need the bullets to have much of a base to ogive difference to go from a jump to a jam. I have recently tested a load that worked well with a small jump, then wanted to try a jam, and had to reduce the powder charge by 1.0 grain (in 6.5CM) to get the same speed. That is a lot.

Try seating the factory ammo 15 thou deeper in the case, it probably will not help if you have a carbon ring, but it could eliminate some possible causes around jamming instead of jumping the bullet.

Have also fired factory ammo before that blew primers on hot days, so it might just be a ‘hot’ (faster burn rate) powder lot, or the factory is putting in a little too much powder in the newer batch. In short, i will be surprised if the rifle has changed mechanically (e. g. a dimensional change in chamber dimensions). On a switch barrel, this is of course possible if you remove the barrel, and then put it back with a way different amount of torque (hand tight vs torqued up to 100 ft lbs). Also note that Hornady brass can have major differences in wall thickness and weight. That will change internal volume some amount, and affect speed and peak pressure. Usually not enough to cause problems, but if the loaded ammo is already at or close to the limit, then that can also help to push the load into over pressure.

My bet is you have a carbon ring. Get a low cost bore scope. New Teslong is superb, and affordable, just search this site.

Hope you get it resolved soon.

 

[NamibHunter]

To check for a carbon ring, you will either need to go see a gunsmith who has a good one, and he will likely charge you more than $50, or you will have to buy a good one and perhaps do some research on the internet to learn what a carbon ring looks like. Older generation Lyman bore scope has fairly poor picture quality, and has now been superseded by this cheap made in Hong Kong device. I got one and it is well made, and it works real well, short focus and a 45 degree mirror. Around $49.

Link to Amazonia:

Amazon.com: Teslong Rifle Borescope, 0.2 Inch Gun Barrel Bore Scope Camera, Side-View Mirror, 36 Inch Semi-Rigid Cable, Works with Windows, Mac and Android Smart Phones: Gateway

Buy Teslong Rifle Borescope, 0.2 Inch Gun Barrel Bore Scope Camera, Side-View Mirror, 36 Inch Semi-Rigid Cable, Works with Windows, Mac and Android Smart Phones: Borescopes - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

About $49.

 

[Pilotscrappy]

So I'm having a similar issue with my mpa 6.5 cm.
I'm in load development and running 41gr of h4350 I'm getting 2810fps with a heavy bolt lift and flattened primers, seating bullet 2.190 cbto

Just for curiosity I bought some factory 140eld match today and ran 20 of them. No sticky bolt but damn my avg fps over the 20 rounds was 2820fps. Should I be concernedwith such fast velocity when the box says 2715fps?

I think I may be jamming the lands with my reloads I'm going to seat bullets deeper into case and see if anything changes.

Anyone else chrono factory rounds 140 eld-m in their mpa?

 

[LawnMM]

If you fire ammo, and there's no pressure signs, be happy you have a fast barrel and go live your life.

Factory ammo tends to be conservative, so it works with everything, if you can't shoot Hornady without pressure signs, try some Federal.

If no factory ammo works, send the gun back.

 

[NamibHunter]

If you fire ammo, and there's no pressure signs, be happy you have a fast barrel and go live your life.

Factory ammo tends to be conservative, so it works with everything, if you can't shoot Hornady without pressure signs, try some Federal.

If no factory ammo works, send the gun back.

Good advice.

Factory ammo is designed to be safe in a min spec SAAMI chamber, which is why it is generally so much slower than properly optimized hand loads. And also why the cases in a box of factory ammo has so much slop, often sized smaller (radius) and shorter case head to shoulder datum line. The slop makes the ammo work in almost any chamber, including the occasionally out-of-spec chambers churned out by the mass producers, but such an approach is inevitably bad for accuracy.

The MPA rifles intentionally seems to be throated and chambered for the factory Hornady 140 grain ELD “Match” ammo. So tigher chamber (minimal gap between case and chamber, for better concentricity), and shorter throat, for a small jump. They seem to be aiming for a jump of around 5 thousands, and definitely no jam. This will also aid concentricity, it will help to build pressure a little more quickly, and help the case neck grab the chamber sooner, and for the case to stop moving (or at least aid in consistent case movement from shot to shot).

My rifle produces similar speed. I have fired a box of Berger 140 Hybrid factory loaded ammo and it averaged 2840 fps. Which i know is fast for a 26” barrel and 140 gn projectiles. Likely they are using a different powder than H4350. [It was also faster than normal in my other rifle, but that gun has a 30” barrel, so not easy to compare].

Hornady 140 ELD-M factory ammo averaged 2785 fps, with a 15 fps SD (not so great). Several shots were above 2800. No pressure signs. Your barrel is a little faster than this, but not that much.

If you don’t see pressure signs like half moon or full moon ejector marks on the brass, and no hard bolt lift, you are most probably ok. [Primer condition is not always a reliable indicator.]

Just avoid shooting factory ammo heavier than 143 gn that will jam the bullet hard into the lands. [That is stated in the MPA manual as well.]

MPA represents a different compromise than what the mass market gun makers like Remington, Savage or Ruger prefer to use, but it is a good approach as long as you understand that the gun has a match chamber optimized for a specific ammo, and that this choice will exclude the use of some factory ammo like the Hornady 147 gn ELD-M. [You could of course reseat factory ammo (deeper) to get back to a 5 thou jump and avoid the hard jam. Just watch out for overly compressed loads.]

Hope this helps.

 

[NamibHunter]

So I'm having a similar issue with my mpa 6.5 cm.
I'm in load development and running 41gr of h4350 I'm getting 2810fps with a heavy bolt lift and flattened primers, seating bullet 2.190 cbto

Just for curiosity I bought some factory 140eld match today and ran 20 of them. No sticky bolt but damn my avg fps over the 20 rounds was 2820fps. Should I be concernedwith such fast velocity when the box says 2715fps?

I think I may be jamming the lands with my reloads I'm going to seat bullets deeper into case and see if anything changes.

Anyone else chrono factory rounds 140 eld-m in their mpa?

Btw: The 40-50 fps of additional speed is very likely caused by the relatively tight chamber. Not a bad thing.

During load development you will use less powder than expected to achieve the speed you want, and pressure signs will arrive a little earlier.

But the tighter chamber enables it to shoot the Hornady factory 140 ELD-M match ammo more accurately. Less slop (gap) between chamber and round. Should also give better concentricity, bullet jump is much smaller (optimal amount of free bore), lead angle is optimized for the shape of the particular bullet, and the brass is probably grabbing the chamber earlier and sealing it better.

 

[NamibHunter]

I realize this is an old thread, but just a quick update on my experience with the MPA BA rifle in 6.5 CM:

A very slight carbon ring appears after 150 rounds, not enough to cause problems, but visible with the bore scope.

I now run an oversize bore brush chucked in a speed controller drill (at very low speed) in the neck of the chamber every time i clean the barrel, for about a minute. That takes care of it.

Same thing happens in my Savage 12, so not unique to MPA.

 

[abn31c]

What powder?

 

[NamibHunter]

What powder?

Moderate load of H4350.

 

[abn31c]

Wow, the only time I've had a carbon issue was with Rl16, good stuff for my hunting load, but not for match or practice. I don't believe the creedmoor case is any more prone to carbon issues than any other similar cases. FWIW

 

[NamibHunter]

Wow, the only time I've had a carbon issue was with Rl16, good stuff for my hunting load, but not for match or practice. I don't believe the creedmoor case is any more prone to carbon issues than any other similar cases. FWIW

Amount of fouling was actually very slight, but enough to be visible via the bore scope. My point was that carbon fouling in the chamber starts building up pretty much from day one shot one, and if you clean it out every time you get home, a real carbon ring has no chance of building up and getting to that ugly rock hard state where it is very difficult to remove. Gradual process but unrelenting.

Yes: Carbon fouling from H4350 is far less than say RL-17 and the other worse offenders. Carbon fouling in this instance might be a bit more than normal because these rounds where loaded to lower pressure (aiming for a lower node) and trying to preserve barrel life. Is your experience also that full pressure rounds seem to burn cleaner?

It took at least 2,300 shots before the barrel started spiking in speed (which turned out to be a very well developed and pretty bad carbon ring). I guess my partial half hearted attempts at cleaning the chamber had some benefit, and the problem slowly built up over time, until it was thick enough to cause a real problem. Hard to know unless you have a good bore scope. That used to be a $1,100 luxury, but Teslong has broken the price barrier (below $100 now).

The amount of carbon in the neck of the chamber between the point where the brass stops and the chamber ends is rather significant in my Savage rifle (i measured it with a Sinclair tool) and is around 0.035” long, also because my brass is a little short. Some Lapua cases came out of the blue box at 1.906”, so i trimmed them all to that length. They are slowly growing at each firing (about 1.5 to 2.5 thou every time). Trying to get back above 1.915” but even then, there is ample space for carbon to deposit. Shooting brass of different case length is part of the problem, something to be avoided i guess.

 

[1moaoff]

Thats acceptable to me. Mine is 2 to 4 inches low at 100. I thought I had it fixed but it came right back. Mine does this on every string of fire, regardless of time in between.

I'm not trying to be silly but 2-4"? Really? You sure it's not cold shooter?

 

[abn31c]

Replaced that barrel about a year ago. Problem solved.