So I built a 6.5g with a Faxon barrel and it seems my rifle will shoot mediocre until the barrel is warm. I'm not sure as I haven't done any definitive testing, I have shot it mostly with temps at or below freezing.

My first 10-15 shots maybe 80-90% will be moa or less with the other shots doubling the group size. This is at a rate of 2-3 shots per minute. Then once the barrel is warm, not hot at all it will keep tight groups. I thought the barrel needed cleaned at first but when I start shooting tight groups after its warm I figured it didn't need it.

The barrel extension to upper fit wasn't tight as in the barrel slide right into the upper. That said it wasn't wobbly, a little bigger and it would have needed pushed in. I was thinking about adding Loctite to the extension or a shim. Not sure, I have never had this issue with a cold barrel. I suppose it could even just be the barrel, or some weird harmonics when its cold.

For example I was shooting steel at 530m and with the first 9 rounds I missed a 16inch gong 3 times. I let my nephew take a few shots then I proceed to hit the 16inch gong twice towards the middle. I then move over to a smaller 9.6x20 silhouette and shoot a 4.5inch 5 shot group.

Maybe its just me, the biggest variable. I haven't been shooting as much lately and I know a semi will really expose fundamental errors in technique.

Any input?

Jeff

You know the Faxon Grendel I put together for my brother for Christmas so far has shown similar characteristics.

Is the barrel fluted?

I have a Brownells 24" barrel on my Grendel and can shoot a 30 shot string with out issue. Though as with all my rifles, I warm them up first then keep them around a certain warm temp for the duration. I monitor with an IR thermometer.

Interesting for sure. Which barrel exactly did you use?

Yes it is the 20inch fluted. Today I shot 27 shots at 1100yards 25degrees with a 10mph or so wind from 1-2oclock, 3-9rd mags. First mag I didn't get a single hit on a 16inch gong but I was very close on all except 1 which was almost 1mil low. 2nd 9rds I went 5 for 9. 3rd 9rds was after I walked away for 10-15minutes and I went 1 for 6 on the gong and 0 for 3 on a smaller 9x20 silhouette. The sun was below the horizon on the last mag so I was having trouble seeing misses.

The barrel did not even reach a lukewarm temp on this session. I need a warm day to see if this issue occurs. I shot once around 65-70 and another around 40 but both of those range sessions I was having issues with my Vortex HST.

Also at 1100yards it could have been me/wind except the 1mil low shot. That's where the lab radar would come in handy, but since I don't know how fast it was going I can't tell.

18" Gunner.  Hoping it's going to settle down some with more rounds through it.  Barrel extension is bedded already with 620.

So you went all out with the high strength stuff I see. Definitely try cleaning the barrel good within the first few hundred rounds. Mine needed a break in period for sure.

I've bedded nearly all my rifles with it.  Even pulled the Larue Grendel apart and bedded it.  It's perfect for the application.  Will take a torch to remove though.

How long do you let it set before shooting? Looks like most of the Loctite(s) say they fully set in 24 hours.

24 hrs on 620.

I use a shim set I got from amazon.  Takes a hammer on a sacrificial muzzle device to install when done right.  No torch on aluminum to get it off  - a scary proposition any day.

A warm barrel Shooting well is odd.  A warm barrel will have a bunch of characteristics that change when warm - and if that is enough to push your accuracy to some strange place I don’t thing anything but replacing it is likely to help.

Odd question. - are you running an AAC can?

No suppressor just a PWS brake. In this instance when I say cold I am talking an ambient temp of 25 degrees and a warm barrel is just barely lukewarm. The barrel when warm is probably not anymore than 70-75.

Do you clean thoroughly the bore after every range trip?  Most barrels shoot like asshole for some number of rounds after cleaning.  Overcleaning is a real concern with precision barrels.

Another thing you could try - find an indoor shooting range.

I do not clean unless I see accuracy loss. I thought about cleaning the barrel again but a dirty barrel shooting bad shouldn't always shoot a good after warming up right? I cleaned the barrel when I first built the rifle and once after a few hundred rounds. After the second cleaning it took about 15 shots before my accuracy came back.

I bedded the barrel last night so I'll shoot it again Thursday morning once it has cured.

Too humid in the South no to clean regularly.  I know he's not but for those that are you will end up with rust if your not thorough with cleaning.

Get the barrel extension hot enough with the torch till the 620 smokes and use a wooden dowl and hammer to push the barrel out.  I tried it on a spare upper and old barrel the other day and it's no problem.

That's why I got the Faxon. So I don't have to keep up on it too much and not worry about corrosion. It is very humid here most of the year, with some dryer weather in the winter.

Yeah it doesn't take much here to get rust started.  I clean every trip.

I have taken the Grendel out some more in this warmer weather we have had and determined this barrel just doesn't shoot well once it starts getting hot. I mean 1-9rd mag shot cold bore in a few minutes my last couple of shots start to wonder. I can get 5 or 6 accurate, precise shots before it gets crazy.

If I let it cool a few minutes between shots it shoots great. I am quite disappointed it shoots like that and am selling it to a friend dirt cheap(he is aware of the history of this barrel) He reloads so maybe he can work something up for it.

My .308 Tikka on the other hand was still shooting a tad under moa at 100m with a barrel almost too hot to touch.

Its likely inherent to the profile of the barrel, which is why for my precision/bench rest gun, I switched to a fat Wilson bull barrel. No more heat/POI problems.

It shoots great until it gets hot and then it'll start to throw a shot half the time. I did not notice it during the winter but have with close to 90 degree temps.

Yep. If you want consistently tight groups round after round, you likely need to switch to a heavy barrel. You wont be disappointed.