Axis Barrel Mod range results.

[BlueDog]

I finally took my Axis 308 with my DIY "straightjacket" barrel experiment to the range. For a reminder here is the rifle:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/D341ED07-5F22-4171-8730-80C12361BA43_zpsjkpj6ddf.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/D341ED07-5F22-4171-8730-80C12361BA43_zpsjkpj6ddf.jpg.html)

http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/8A705E74-8B4C-406A-9022-EBD2F546C838_zps4rcboof9.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/8A705E74-8B4C-406A-9022-EBD2F546C838_zps4rcboof9.jpg.html)

The rifle is an Axis SR 308, (threaded pencil barrel) with a 1.25" titanium sleeve (0.028" thick) filled a thermal conductive potting epoxy. I have some detailed pics if anyone would be interested.

Here are the 100 yard results:

168gr Federal Gold Medal Match -3 round group.
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/E44E5C9F-A71E-4183-BBE0-B124A88BAED4_zpsgymb8wjw.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/E44E5C9F-A71E-4183-BBE0-B124A88BAED4_zpsgymb8wjw.jpg.html)

168gr Federal Gold Medal Match - 5 round group
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/6012B2FA-D59B-4747-8BB3-DE471E6B20A8_zpsmmxs796a.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/6012B2FA-D59B-4747-8BB3-DE471E6B20A8_zpsmmxs796a.jpg.html)

175gr HPBT Silver State Armory - 3 shot group
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/C7594738-E0A2-4889-ACB9-25EBF3D3C05D_zpsbp4aeom1.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/C7594738-E0A2-4889-ACB9-25EBF3D3C05D_zpsbp4aeom1.jpg.html)

175gr HPBT Silver State Armory - 5 shot group
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/01B050D5-6225-4856-90D3-78990CCCDB93_zpsnil9wal8.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/01B050D5-6225-4856-90D3-78990CCCDB93_zpsnil9wal8.jpg.html)

In total we shot 60 rounds through the rifle, and groups didn't open up after a few short rounds like the pencil barrel did before. I did not let the rifle cool between groups (other than the time it took to waddle down to the target and back). I am pleased with the results, ecspecially with factory ammo. This rifle is still new, and I hope with some load development I can shrink the groups some more.

[Rosco]

Excellent shooting, and great looking rig!! You should send Jeff the picture and groups so he can post it on the CDI page. He asked me to send him some but truth is your rifle is much sharper looking than mine.

[devildogandboy]

pretty impressive results, good shooting.

Bruce

[BlueDog]

Thanks guys, it should settle in with a few more outings. I'll continue to try a few more factory loads (175 FGMM, Black Hills, etc) and see if they shoot well. Then, I'm off to find a longer range. I wish they'd cut our hayfield!

[DrThunder88]

Your pseudo-Strait Jacket is one of the coolest mods I've seen done to an Axis. Really nice work!

[klr]

Nice. How long is your barrel and what does it weigh?

[BlueDog]

klr, the barrel is 20", and the titanium weighs practically nothing, but the epoxy added about a pound. The epoxy is a potting compound that is thermally conductive, which has a high percentage of aluminum powder in it. The straightjacket ($$$) people really brag about the thermal wicking power of their proprietary media. I was going to add copper granules as I believed they were the most thermally conductive material. However, in my research I found that diamonds are far (3-4x) more thermally conductive than copper. I learned something I didn't know! So I added 200 carats of 50,000 mesh (0.5 micron) synthetic diamond powder. I'm not concerned about the heat, but I wanted to see if I could replicate their offerings cheaper. Less than $100 vs over $800.

[klr]

Thanks for the info, BlueDog. I'm not trying to be critical, but I'm trying to see the benefit if you add a pound of epoxy. What is the advantage of making a barrel this way vs a normal heavy barrel? Heat dissipation for long strings of fire? Thanks.

[Robinhood]

Copper retains heat where the less dense aluminum dissipates it. You made the right decision leaving it out.

[BlueDog]

klr, I believe it was less than a pound, however the theory is a 1.25 solid barrel is far less "stiff" than a similar sized laminated barrel. (Plywood vs a pine board). The epoxy pulls double duty in that it does allegedly pull heat away from the barrel but moreover (and my focus) it dampens the barrel harmonics (barrel whip). I was very interested in the straight jacket system when it first came out, but their price has risen to a point to where I couldn't justify it. ($849 for their titanium jacket) I did this build as merely an experiment to see if I could replicate their awesome system and results.

[BlueDog]

Robinhood, I disagree (kind of). Thermal conductivity is measured in units of watts per metre per Kelvin. Usually seen noted as W/(m K) units.

Aluminum = 205 W/(m K)
Copper = 401 W/(m K)
Diamond = 1000 - 2300 W/(m K) depending on purity

Aluminum is more widely seen in consumer based thermal heat products due to relative cost, as aluminum is far cheaper than copper. Copper would retain heat longer due to the higher mass versus aluminum, but I think the copper would transfer the heat to the outer tube faster, and the heat then would be dissipated into the air. Right?

[Rosco]

So the barrel diameter is 1.25''? And post some pics of the mod it is really neat.

[BlueDog]

Here are the pieces before the assembly:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/6FE059CB-5C5A-4FB9-8EF7-BB3BCC5DF3EF_zpsrqqdypem.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/6FE059CB-5C5A-4FB9-8EF7-BB3BCC5DF3EF_zpsrqqdypem.jpg.html)

For the muzzle end, I needed a thin stainless washer with a diameter of 1.194, I have no access to a lathe, so I chucked up the washer in my drill press and filed to final diameter:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/1EDAD541-F839-465F-884E-DF5136A40BA5_zpspvk7mvdj.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/1EDAD541-F839-465F-884E-DF5136A40BA5_zpspvk7mvdj.jpg.html)

If I had to do it over again, I would have had the barrel nut turned down for a press fit. The titanium tube was epoxied to the barrel nut, and the muzzle end center was located with the locking nut from the muzzle break. Here it is right before adding epoxy:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/E47338BB-CAB0-48DA-ABC1-272765B7F684_zps0avj2hox.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/E47338BB-CAB0-48DA-ABC1-272765B7F684_zps0avj2hox.jpg.html)

I researched high and low for a the best potting compound. The particular brand I used touted high pourability, high heat transfer, 500°F durability, and has a cured durometer (Shore A) of 85, which is approximately like a boot sole. As per the discussion above, I added the diamond dust for superior heat transfer:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/428DFB15-F6C5-454F-8CD4-3BFD61663CD7_zpscnssexcd.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/428DFB15-F6C5-454F-8CD4-3BFD61663CD7_zpscnssexcd.jpg.html)

The potting compound I wanted must be for industry only, as I could not find any for sale, however the website said "call for free sample". I did, and a very nice gentleman took my info and sent me a free sample which consisted of a quart can of Part A and a quart can of Part B! I only mixed up one cup for the barrel, so I have plenty for more experimenting. The directions were simple, a 1:1 mix. I added the 200 carats of diamonds and mixed well. It had lots of bubbles, and the directions call for putting it under a vacuum for 10 minutes to rid it of air. I don't have a vacuum pump, so I poured the mixed epoxy into a plastic container and placed the plastic container in a wide mouth quart jar, and used my wife's vacuum sealer that has the jar attachment (in sure she wouldn't mind...) From my research, Foodsavers pull about 21 pounds Hg of vacuum, and WOW did it work well. I ran the machine after it would sit for a minute or so, I open the jar, then vacuum the air out again. Here is my setup:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/DF12A028-5B51-4856-80B9-1A9A15FB0BAC_zps2y3iabnb.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/DF12A028-5B51-4856-80B9-1A9A15FB0BAC_zps2y3iabnb.jpg.html)

As the potting compound was in the jar under a vacuum, I fashioned a makeshift funnel from a water bottle and taped it on. I also taped up the threaded portion of the barrel. Then I poured the mix in! It poured well even with the addition of the diamond dust. Once to the top I removed the funnel and put my thin washer on, ran a thread protector nut down tight, cleaned up the squeeze out, and waited. Here is the pour:
http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/AA538E2A-F5AA-463E-866E-02B5FFDB7836_zpsz0f5auto.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/AA538E2A-F5AA-463E-866E-02B5FFDB7836_zpsz0f5auto.jpg.html)

[Rosco]

Impressive! Very well thought out and creative. I would be curious to know the temps inside your chamber vs. a standard Axis after say a 5 round string.

[BlueDog]

@Rosco, I wish I had brought a thermometer to do some tests. I did have my HogHunter with us as well, and it was shot along side this rifle shot for shot. (It too shoots very well). At the end of our session the barrel on the HH was very warm to the touch, and the Axis was not nearly as warm. As for the chamber, the pinky test (not very definitive) again showed a marked difference in temps. It wasn't very scientific, but it should be a close sample, as both are 308's, both are 20" barrels, and both are 1:10 twist. Both rifles shot exactly the same loads for the exact same number of shots. I hope to shoot at a longer range soon and I will report any results, good or bad!

[DrThunder88]

A few more questions came to mind while I was out and about today. I hope you don't mind.

Because the compound is flexible, is the jacket assembly removable? I imagine prep work would have been needed to release the barrel from the jacket, but is there enough give to slide the muzzle flare through the potting epoxy? I'm thinking of how you might replace the barrel at the end of its life, though I imagine the system extends barrel life. The SR barrel would obviously limit your options for swapping later on, but I could see how a standard sporter barrel would be easier to interchange. A coating of silver heat transfer paste might keep the conduction pathway open during barrel swaps.

Was the barrel still bearing the factory finish when you encapsulated it? I'm wondering how, if at all, that might affect your system's performance.

[BlueDog]

Dr. Thunder, I welcome all questions. Yes the epoxy is flexible, I poured the excess into a silicone mold. So I have a solid 'hockey puck' of this material. It is pretty amazing stuff, it's supposed to have a durometer rating (Shore A) of 85. Which according to a chart I found on the interwebs is similar to a sole of a sneaker, which it seems to be.

The jacket is not removable, as the potting compound bonds to the barrel and jacket. I cleaned both the barrel and jacket (inside) with a acetone to insure a good bond. I think the bond would help with rigidity and heat transfer. The sole reason for choosing the weird blunderbuss profile of the SR was the sporter contour with a threaded muzzle (which I wanted to help locate the center and to help cap the end). TTI says they turn down barrels to the absolute minimum SAAMI allowed diameter before adding the jacket.

As as for life of the barrel, I hope I can get similar results to the Straightjacket. They have found an extreme prolonged life of their jacketed barrels. Reportedly, TTI has test rifles that have upwards of 20,000 rounds put through them with no measurable chamber erosion. They also did 13 (30round) mag dumps through an AR-15 in just over 3 minutes and the chamber temp was only 207°! I'm not concerned about "reusing" this jacket assembly, it was quick to make and relatively cheap. If I was to replace the barrel I'm sure it would be a matter of cutting the jacket back enough to loosen the nut. My first idea was to have a false shoulder to facilitate removal, but I soon thought it would be too expensive and a contrived mess. I then noticed TTI also jacketed to the barrel nut. I really would like to have one of their barrels.

This reminds me of a quote in someone's signature line in another forum (paraphrasing): "when debating round count for a new barrel, someone asked when I swapped mine out. I replied 'I don't swap barrels, I shoot a 308."

[doodedge]

Very impressive!

If you don't mind, what prep did you put into the action side of the barrel before pouring? I saw that you said you wished the barrel nut was tapered so you could get a press fit... so did you just slide the titanium tube down to the barrel nut and then tape it off before pouring or was the tube tight enough on the barrel at that point that you didn't need to?

Also, was there any major thought process behind going with the titanium tube other that sweet looking rig?

Thanks very much, and great job!

[BlueDog]

Doodedge, my thought process was hopefully replicating the TTI "StraightJacket Barrel" system they offer, and more importantly replicate their results. Which I always thought were very impressive. There is a pretty glowing write up on 'gunsamerica,com' if you are interested in the StraightJacket. The reason I used titanium was that's what TTI uses, no other reason. (Other than its space age cool!)

The barrel nut is tapered already from the factory, I wished I had spun it off and had it machined back to a straight sided cylinder so the tube could set against a shoulder. As is, it was a pretty solid lock up and I had a light press fit as is, but with a taper it leaves much to be desired. As for prep, I roughed up inside the tube as much as possible, and used the corner of a file to cut several grooves in the corresponding area on the barrel nut. I then epoxied the tube to the barrel nut with JB Weld, then ran the muzzle brake nut against the tube to hold it together. The next day unscrewed the muzzle brake nut and found the tube was much more rigid/stable than I had hoped. I then poured as described above.

I do hope to shoot this at further distances soon, but with all the crops in, I'm am struggling to find a place to add more data to the experiment.

[BlueDog]

With the hayfield finally mowed, we tried the Axis barrel mod at 300 yards. Keep in mind this is still factory ammo, but it is FGMM. Interestingly the two groups are the same gun, same point of aim, different shooters. My brother's group is on top, mine is on bottom shot immediately after he did. The group was just over 2 inches. Nothing groundbreaking, but still pretty good for a factory 20" barrel with factory ammo.

http://i1065.photobucket.com/albums/u390/ThirstyDogBlue/49A59CDA-6532-433A-B66C-2E587BF695BD_zpsmbd090nq.jpg (http://s1065.photobucket.com/user/ThirstyDogBlue/media/49A59CDA-6532-433A-B66C-2E587BF695BD_zpsmbd090nq.jpg.html)