MPA Chassis and Large Barrel Contours

[Bryan Z.]

I have the first gen MPA chassis (see pic) and dropped a MTU barrel in there. I was able to fit two pieces of paper in between the top (NV mount) and bottom channel area but when I went to three, it got clogged. I loaded some rounds for load development (see pic) and got some good groups at the lower charge range but the groups expanded quite a bit at the higher charge range (up to 43gr) I plan to continue working up the load because I had zero pressure signs at the highest charge. However, I wonder if the poor grouping at the higher charge is because the barrel may be contacting the chassis?? I do not want to do any smithing work so am thinking:
1. Pull off the NV mount
2. Pull off the NV mount and fit a hard plastic between the lower barrel channel and the barrel; I would use the same type of plastic I use between my barrel and barrel block when I bolt down my unlimited barrel into my barrel block on my rail gun.
3. Leave it all and put plastic between the barrel and channel.
4. Do nothing and see how the higher charge loads do.

Any ideas, advice, etc. is appreciated.

 

[Thud]

Maybe your load is the 41.6 or 42 gr.
it's the higher load not the barrel contact as there is none.
Leave the plastic out.

 

[TC]

I spoke to Phil Cashin about barrel profiles a couple of weeks ago and he said using an MTU profile isn't an issue for the MPA in terms of clearance.

 

[ballison]

I've run MTU and heavy varmint barrels in MPA chassis, and never had an issue

 

[Nightraider]

I've run MTU and heavy varmint barrels in MPA chassis, and never had an issue

Same here

 

[Bryan Z.]

Thanks all for the inf

 

[lawrence97]

I have the first gen MPA chassis (see pic) and dropped a MTU barrel in there. I was able to fit two pieces of paper in between the top (NV mount) and bottom channel area but when I went to three, it got clogged. I loaded some rounds for load development (see pic) and got some good groups at the lower charge range but the groups expanded quite a bit at the higher charge range (up to 43gr) I plan to continue working up the load because I had zero pressure signs at the highest charge. However, I wonder if the poor grouping at the higher charge is because the barrel may be contacting the chassis?? I do not want to do any smithing work so am thinking:
1. Pull off the NV mount
2. Pull off the NV mount and fit a hard plastic between the lower barrel channel and the barrel; I would use the same type of plastic I use between my barrel and barrel block when I bolt down my unlimited barrel into my barrel block on my rail gun.
3. Leave it all and put plastic between the barrel and channel.
4. Do nothing and see how the higher charge loads do.

Any ideas, advice, etc. is appreciated.

What is your freebore? Those top charges Above 41 seem to be high according to Hornady manual.

 

[Bryan Z.]

I spoke to Phil Cashin about barrel profiles a couple of weeks ago and he said using an MTU profile isn't an issue for the MPA in terms of clearance.

The profile I have is a 1.25 for 5 and then taper to 1 with a finish length of 27. Most MTUs taper to .83-.9 and fl at 26.

 

[coldboreshot]

Maybe your load is the 41.6 or 42 gr.
it's the higher load not the barrel contact as there is none.
Leave the plastic out.

^^^^^^^^^^^^^ harmonic sweet spot

 

[willbas]

I have a Heavy Varmint 1.25 to 1 inch at 32 inch cut to 30 Inch I have full clearance I just can not add the Spigot Mount V4, paper just hits at the beginning of the mount

 

[Bryan Z.]

I have a Heavy Varmint 1.25 to 1 inch at 32 inch cut to 30 Inch I have full clearance I just can not add the Spigot Mount V4, paper just hits at the beginning of the mount


View attachment 1170303

And no possible issue with the barrel touching the chassis? Notice any irradiated groups, etc.?

 

[willbas]

And no possible issue with the barrel touching the chassis? Notice any irradiated groups, etc.?

with out the spigot mount paper moves all the way to the action. 300 yard 15 rounds shoot group the top 4 were all my fault.

 

[Delfuego]

I have 3 MPA's and they all have Heavy Varmint or M24 currently. The HV are a tight fit for sure, but no issues. I don't use the NV bridge. I also have no interference with the spigot (older one-sided).

I personally would shoot that 41.6 till the wheels fall off. Don't over think it. Don't chase a higher node. Shoot and have fun. Most people shooting 6 creedmoor would love that group.

 

[Bryan Z.]

I have 3 MPA's and they all have Heavy Varmint or M24 currently. The HV are a tight fit for sure, but no issues. I don't use the NV bridge. I also have no interference with the spigot (older one-sided).

I personally would shoot that 41.6 till the wheels fall off. Don't over think it. Don't chase a higher node. Shoot and have fun. Most people shooting 6 creedmoor would love that group.

Good advice Delfuego!

 

[rardoin]

The current F-TR 1000yd champion won using a MPA chassis. I shot the gun yesterday and it appears that the barrel contour is much like Wilbas gun. That gun will flat out shoot. Saw @Down South shoot a clean with 9x firing a test load (20rds) at our 965yd range. I’m pretty sure the barrel was not slapping the chassis

 

[Bryan Z.]

Thanks all for the replies. Looks like there isn’t any interference in the fit with this heavy contour. I took some 42grs out today and they shot really well and chrono’d at 3149 (5) so I’m nearing the velocity max for the NRL and PRS matches I plan to do so I’ll stop there. Thanks again for the wisdom!

 

[DukeDuke]

so a straight 1.25 should be ok?

 

[Down South]

The current F-TR 1000yd champion won using a MPA chassis. I shot the gun yesterday and it appears that the barrel contour is much like Wilbas gun. That gun will flat out shoot. Saw @Down South shoot a clean with 9x firing a test load (20rds) at our 965yd range. I’m pretty sure the barrel was not slapping the chassis

Yeah, that gun shoots pretty good............The barrel in that black chassis i used at nationals last year is 5 inch 1.25 then straight tapers to .950 at the crown (30 inch barrel). The other chassis we shot has a heavy varmint contour barrel that tapers to .900 at the crown. Both chassis have enough clearance but when i had MPA send them to me i told them what contours i'd be running, not sure if they modified them a little to take the bigger contours.

 

[Delfuego]

so a straight 1.25 should be ok?

I don't think that will fit. I think the heaviest contour that fits is the new Proof Competition Contour. I would reach out to MPA or measure yours to make sure.

FYI: There are a few different iterations/generations of MPA chassis. They are all a little different and they improve them a little each time. Mine are 2nd & 3rd gen MPA Competition Chassis.

 

[Forward543]

I shoot a straight 1.25 in an moa comp. I had to pull the nv bridge, and open the channel a little, but it works. I also epoxy bedded the action in, which helped with a floating zero.