Thinking of building an F-TR gun with an Accuracy International AT

[jlow]

Brought this gun for fun and also shooting PRS matches. As you can imagine, it is super accurate and robust. One super nice thing about the gun is it has a switch barrel capability which means a user can switch barrel in a few minutes and at least with the two barrels I have – 24” .308 and 26” 260Rem, the gun’s POI literally does not change when switching barrels. Right now I am wondering if I can also use this chassis for shooting F-TR matches since there is a limited number of local PRS matches I can get into.

To do this, I will mount a NF competition scope and put on a 30” .308 barrel. I have weight the gun and with the 18.15 weigh limit in mind and it looks like it would make weight if I use something like Medium Palma or even a Whitney Med. Palma barrel reamed to shoot the 215 Berger Hybrids.

My question to the folks who shoot F-TR is what do you think of this plan? I realized this is not a purpose build F-TR rifle but what are my limitations? Any suggestion on barrel twist or even an alternate bullet?

 

[dcali]

That's doable, but weird. I'm not sure I would spend that kind of money on a scope only to use it on a sub-optimal rifle. You may was well go cheap and get a fixed weaver or sightron, because the scope won't be what's limiting you. For my money, I'd build a whole new rifle and do it right.

The 215's are tricky. The 185 Juggs are a lot more forgiving in my experience. The extra recoil from the 215s seems to play havoc with vertical with those long skinny barrels. That's my theory at least. I was stubborn, and started with the 215's and was humbled by how difficult they are to shoot consistently. I still have a few hundred, and I will eventually figure out how to shoot them, but for now, I'm using the 185's and I'm shooting better scores than I could with the 215's. Random vertical really eats into your scores.

 

[Ned Ludd]

I would ask you the question, "Why not?". I know a few people that shoot similar setups and they do fine with them at the local, and occasionally regional, level. But the fact is they wouldn't likely be winning a National Championship regardless of what setup they were using. Very few have the skill to consistently compete at the very top level. So if you want to shoot in local or regional F-Class matches, by all means you should do it, but have reasonable expectations when you first start out. It might be that once you try it, you''l be hooked like many of us. At that point, if you feel you need a better setup, it won't really matter because once you're hooked, you'll give up a kidney to get what you want .

In terms of setting up the rifle, the question I would ask first is what matches do you have access to in your area, meaning 300 yd/600 yd/1000 yd? If you're never (or only rarely) going to shoot at 1000 yd, I wouldn't bother setting up the rifle to shoot 215s for the reasons damoncali mentioned above. If you're shooting only at 300 and/or 600 yd, 185 Juggernauts, 185 Hybrids, or 200 Hybrids should be more than adequate for the task. Of those three, you really want a 32" barrel for the 200 Hybrids. You'd be giving up a some velocity and performance with the 200s using a 30" barrel, although it would work if necessary. On the other hand, either of the 185s can be pushed to the 2750-2780 fps range from a 30" barrel with no trouble, and the 30" barrel would represent a weight savings if the rifle is close to max. The 185 Hybrids won't be all that far behind the performance of the 200 Hybrids at that velocity. The Juggernaut would be slightly farther back in terms of wind resistance, but still a contender. Further, the Juggs are very forgiving to tune. For either of the 185s, PTG sells a reamer with 0.168 freebore that has been optimized for the Juggernaut, but would work for either. It's a tick shorter freebore than would be optimal for the 200s, but could still work for those as well. If you're working up a load from scratch, I would recommend using Palma brass and small rifle primers because pressure and brass life are less of an issue. In any event, you have several fairly straightforward ways you can go, but one of those three bullets is likely your best bet. A barrel contour that will allow you to make weight is another important concern, then get it chambered optimally for the bullet(s) you intend to shoot. Good luck with it.

 

[jlow]

Thanks for the response guys – much appreciated!

First, the cost of the scope for me is not a problem. I won’t say I am rich but I am retired and this is really my “expensive” hobby and well I have started with the low cost stuff in the past and pay the price. So nowadays, I don’t really go that way anymore. In the end, I am old enough to know that I cannot take it with me…

I have shot the 185 Jugs out of the factory Luther Walter 24” 1:12 twist barrel and they do shoot well. Easy to tune but of course they are not exactly moving out of that barrel fast at only around 2,650 fps.

I have zero vision of shooting/winning a National Championship simply because 1) I shoot too many different types of gun matches ranging from handgun/2-gun/LRP, and 2) I don’t want my shooting to resemble work which it needs to be if I am really serious. Regardless, I normally do well in most of the events I shoot in having recently come second in my local IDPA state handgun match and top dog in a number of 2-gun matches. So I am serious in terms of doing the best I can because I always see matches as competing against myself, learning experiences, and trying always to do better.

Yes, I don’t see this gun as being the end all, just a way to get into the game. First, the barrel is not going to last forever and the scope can be moved to a real F-TR rifle if I really get hooked. So I don’t see much danger there in terms of investment.

The distance question is a good one. There are no local 1k matches, only 600 yards ones. However, MI does have F-Class matches in Grayling and Cadillac which are 1K… So the practice matches are 600 but the real matches are indeed 1K and so because of that, it would seem to make sense going for the 215s since it would not make too much sense to set the gun up for practice range but find that it cannot perform at a real match? Again, not locked into that bullet but at least going by the above logic, that seems to be the way to go?

Weight is indeed a factor and I am pretty sure I will be limited to a 30” barrel. Any suggestion for a reamer for the 215s? Twist rate? Can you guys also give me an estimate of barrel life?

 

[Scott Harris]

Brought this gun for fun and also shooting PRS matches. As you can imagine, it is super accurate and robust. One super nice thing about the gun is it has a switch barrel capability which means a user can switch barrel in a few minutes and at least with the two barrels I have – 24” .308 and 26” 260Rem, the gun’s POI literally does not change when switching barrels. Right now I am wondering if I can also use this chassis for shooting F-TR matches since there is a limited number of local PRS matches I can get into.

To do this, I will mount a NF competition scope and put on a 30” .308 barrel. I have weight the gun and with the 18.15 weigh limit in mind and it looks like it would make weight if I use something like Medium Palma or even a Whitney Med. Palma barrel reamed to shoot the 215 Berger Hybrids.

My question to the folks who shoot F-TR is what do you think of this plan? I realized this is not a purpose build F-TR rifle but what are my limitations? Any suggestion on barrel twist or even an alternate bullet?

To get you started, shoot what you have. AIs are great guns and you can do well with them as is. Now would i spend money putting a custom f tr barrel on it? Definitely not. Its too heavy of a platform and does not ride the rear bag well. For F-TR, a heavy palma is the lightest contour you should use and an AI simply does not allow this. regarding your switch barrel comments, any rifle can easily switch barrels...nothing special there

 

[jlow]

I guess I am surprised but interested in hearing more.

Would like to hear more from people as to how much difference a Heavy Palma makes say compare to a Whitley Medium Palma, there is only a one pound difference between the two.

Would also like to hear why “an AI simply does not allow this”?

 

[Cujo]

I've been shooting an AI AT in FTR for the past 16 or so months. The barrel is a 30" Whitley medium Palma (1:11 twist) to make weight. The weak link is the spigot mount for an Atlas bipod that tends to loosen up during a string. My AT is one of the early ones manufactured in 2014 that has the large firing pin. I've heard of pierced primers with brass that uses a small rifle primer so that means the .308 Palma brass is a no-go for me. Current AT's have addressed that issue.

 

[dcali]

Sounds like you're on the right track. There's no reason you can't shoot a good score with your plan, the gun handling will just be a little more difficult than it would be with a dedicated TR setup. The competition is a great scope. I don't think you need a heavy palma. I shoot a medium palma (because it's a converted palma rifle), and manage to do ok with it. (My next barrel will be a heavy palma, but it's no where near the top of my list as to things that will improve my shooting).

 

[jlow]

Cujo – Very god to hear someone is already doing this and looking at exactly the same barrel. Completely agree about the spigot mount, I’ve been fighting that a bit. Thinking a bit of green Loctite on the thread might help. Mine is also a 2014 AT and yes I have heard all about the 6.4x48L small primer problem. I will probably start with the LP Lapua case which I have lots of. Can you please tell me what bullet/powder you are using?

Damoncali – thanks for the encouragement and experience on the Medium Palma barrel. In the end, it is never going to be the ultimate F-TR rifle but of course I am hardly the ultimate F-TR shooter so this seems like a reasonable gun to get started.

 

[Cujo]

I had Gradous rifles in GA chamber the barrel. I'm using 155 Scenars and 185 Juggernauts both with Varget. Lapua brass and FGMM LRP. I had a bunch of 155's laying around and bought a ton of the 155 Scenar L's because Grafs had them on sale for $299/1000. The 155's at roughly 2,950 and the Juggernauts at 2,730 FPS. My personal best with the AT was a 585-21X (3X600) but that was a fluke. Most of the time I'm in the low to mid 570's with low X count.

 

[jlow]

Thanks Cujo - much appreciated!

Honestly, after listing to all you folks about the difficulty shooting the 215 gr Bergers, I am seriously considering the lighter weight bullets. Since I already have the 185 juggs, that seem to be the way to go but I am debating a bit about the 185 Hybrids.

 

[Cujo]

When you get your barrel chambered, throat it to at least .150". That'll give you a little bit more room. Mine has a short throat (around .100") and my max COAL for the 185's is roughly 2.93" and for the 155's is 2.85" (if memory serves). It shoots fine, however. Mag length is roughly 2.98".

One guy on another site has fabricated a mount that replaces the OEM spigot assembly on the AT. You have to drive out a couple of roll pins to replace it. It has an integrated Picatinny rail which locks the bipod in solid. That modification will undoubtedly be better suited for FTR if that's the direction you want to go. You can always revert back. I don't have it and just use the spigot mount.

 

[jlow]

Cujo – if you have a short throat and your max COAL for the 185 was 2.93” that is very similar to my AI AT factory .308 barrel max COAL for the 185 Juggs was around 2.943” So having the barrel chambered longer i.e. with a .150” throat, that would certainly allow the bullet to be seated significantly longer for more powder and lower pressure, but the round would not fit in the mag right? So the thought is basically to be able to build a longer round for single load that can hold more powder and have a lower pressure? I think this is what you are saying but just checking to make sure I understand.

My MV with the Jugg in the 24" AT barrel was around 2,630 fps and I think just lengthening the barrel by 6" to 30", my MV should be close to 2,730 fps. How much more MV do you think I can get with the longer COAL?

Thanks for the tip about the mount. I think I saw that at the other site. Might be the way to go.

 

[Auto-X Fil]

Right, if you go 0.150" or more, you may not get the 185s into the magazine. For F-Class, single loading is great, and the velocity will be welcome.

Assuming you have a PRS load that shoots well with a jump, then you're fine. However, you might spend some time chasing down a bullet that will do that. It seems like a ton of work for a few fps. If it was a dedicated F/TR rig, then throat so the juggernauts have the BT ahead of the shoulder/neck junction. Every little bit counts, and there's no downside.

But, for a combo PRS/F-class gun, my preference would be to load the Juggernauts to max mag length with 0.020" wiggle room (to seat into, or chase the lands, although this is a .308 so that should take a while), and get the barrel throated to match your dummy round.

Doing that, you will give up a little velocity, but can shoot the same round for PRS and F-class. I think jumping back and forth between loads can hinder really learning the gun and dopes, especially in something dynamic like PRS.

Will this gun be a major contender in either class? No. But it'll be 95% at both, and you will become very good at knowing your rifle in many different situations.

 

[Cujo]

Yes, that's correct. You have up to 2.98" COAL to play with if you want to be able to feed from the mag. I have roughly 2,000 rounds through it spread out among 3 barrels. With the 30" barrel, I can't recall ever feeding it from the mag. It is F Class after all.

With the longer COAL, with my lot of powder, you might get another 25-30 FPS. The next node is not even a consideration for me. I'm running a load at a pressure that I'm comfortable with and I'm good with 2,720-2,730 with the 185's. However, IMHO the longer coal will give you that slight bit of extra headroom if you need it.

 

[jlow]

Auto-X Fil – A lot of options which is why I am here looking for advice. So keep them coming!

For PRS they have the new tactical division that I could shoot the rifle as a .308, but I think the 30” barrel made for F-TR would likely be a mis-fit for PRS. The reason is first of all it will be very difficult to maneuver and even though it will give me additional MVs, not having a comp on the end would make spotting shots difficult. I of course still have my AI Luther Walter 24” .308 barrel which I could use if I want to shoot .308. For PRS, my present plan is to shoot my 26” .260Rem barrel/140 Hybrid combo.

Not too concern about it being major contender in F-TR, mostly get my feet wet and reasonably competitive I think would be good.

Cujo – I can certainly go for the longer throat/COAL, but my question is would there be any downside? The mag fit question set aside, to keep the jump reasonable, the bullet would have to be seated pretty long and so unless I can actually use the space in the case to go to the next node, not sure if that empty space would be a plus or minus.

As you know, accuracy nodes are discrete and the next node is likely too far off to reach and so the additional 25-30 fps that one could get putting more powder in would that be theoretical or actual? I look at it this way, my current accuracy node in the 24” barrel is at 44.3 grain with MV=2630 fps. So assuming the node does not change with the 30”, I get around a 100 fps bonus for the extra barrel length so now I am up to 2730 fps. But if I add 50 thousand to the throat and add 25-30 fps to my MV, would that not take me out of the node since that would change my barrel time? Not sure I can get my head around how that can be taken advantage of?

 

[Sheldon N]

As you know, accuracy nodes are discrete and the next node is likely too far off to reach and so the additional 25-30 fps that one could get putting more powder in would that be theoretical or actual? I look at it this way, my current accuracy node in the 24” barrel is at 44.3 grain with MV=2630 fps. So assuming the node does not change with the 30”, I get around a 100 fps bonus for the extra barrel length so now I am up to 2730 fps. But if I add 50 thousand to the throat and add 25-30 fps to my MV, would that not take me out of the node since that would change my barrel time? Not sure I can get my head around how that can be taken advantage of?

If you don't have Quickload it's hard to model OBT nodes.

The optimal barrel time for each barrel length is different. So a 30" barrel has a different optimal barrel time than a 26" barrel, even if the resulting velocity from their respective nodes is similar. There's a chart out there that lists all the barrel time nodes.

The way that case capacity (through throating/seating longer) factors into this is kind of interesting. If you throat longer and have more case capacity in order to hit the same barrel time it requires more powder, but at a lower max pressure, and with a higher resulting velocity than if you'd started with a shorter OAL.

Here's some modeling info from Quickload. The OBT 30" barrel node #4 equals 1.368 ms. 185 Juggernaut, Varget powder loaded at 2.8 OAL and 3.0 OAL, both loaded to reach a barrel time of 1.368 ms.

2.8 OAL = 43.1g, 61.7k PSI, 2719 fps
3.0 OAL = 45.2g, 60.4k PSI, 2751 fps

Both are "in the node" and have the same barrel time but the longer OAL case gets you more velocity because the rate and duration of acceleration are different.

 

[jlow]

If you don't have Quickload it's hard to model OBT nodes.

The optimal barrel time for each barrel length is different. So a 30" barrel has a different optimal barrel time than a 26" barrel, even if the resulting velocity from their respective nodes is similar. There's a chart out there that lists all the barrel time nodes.

The way that case capacity (through throating/seating longer) factors into this is kind of interesting. If you throat longer and have more case capacity in order to hit the same barrel time it requires more powder, but at a lower max pressure, and with a higher resulting velocity than if you'd started with a shorter OAL.

Here's some modeling info from Quickload. The OBT 30" barrel node #4 equals 1.368 ms. 185 Juggernaut, Varget powder loaded at 2.8 OAL and 3.0 OAL, both loaded to reach a barrel time of 1.368 ms.

2.8 OAL = 43.1g, 61.7k PSI, 2719 fps
3.0 OAL = 45.2g, 60.4k PSI, 2751 fps

Both are "in the node" and have the same barrel time but the longer OAL case gets you more velocity because the rate and duration of acceleration are different.

Thanks Sheldon! You are absolutely correct. What I forgot to take into consideration is the fact that the case volume will increase with the increase in COAL, and that affects a lot that has to do with combustion and pressure. The fact that you can add more powder but resulting in higher MV but lower max pressure is wonderful – sounds almost like cheating!

I actually do have QuickLoad and have found it very useful in finding accuracy nodes. What I have not done with it is to do simulations in situations like this. Part of it is a concern that the numbers are not going to be accurate since I don’t have powder weight/MV data to tweek, but the reality is the actual numbers don’t have to be accurate as what I should be looking at is relative changes when everything is held constant and the only change is barrel length and COAL…

So thanks for pointing this out and doing the simulations. I’ve now done a few and you are absolutely correct so a longer throat will definitely be on the list.

 

[Sheldon N]

Glad to be of assistance! Yes, the load data probably isn't going to be correct until you get all the settings tuned to your load, but it's great for "what if" questions.

 

[jlow]

The new NF Competition and Seekings rings are in as are a bunch of the Berger 200 hybrids. Reamer is on its way to my smith and the barrel have been ordered.

I shot with the scope yesterday and is really impressed with the scope's image quality. It also passed the tall target test with flying color.