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Raptor LRSS progress report....

 
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Old 02-23-2010, 03:22 PM
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Raptor LRSS progress report....

TO all interested.

Its been a few weeks since I returned from the first field test with the new Raptor LRSS in 338 Allen Xpress. The hunt was a success but before the hunt I was really rushed for time getting ready. When I got back I had to put alot of time into the shop to try to catch up from being gone for a week.

Over the past couple weeks, I have been able to take the rifle out for some more testing in more favorable shooting condiitions and have learned ALOT about the initial prototype, some very good, some not so good and an issue I found that had to be corrected.

First the very good. Out of a cold barrel, this rifle, shooting the 300 gr SMK at 2980 fps has to date shot 11, three shot groups at ranges from 1200 to 1550 yards that measured under 5" ctc. I am very happy with that. The design performs very well and is obviously very stable and rigid, at least with a cold barrel.

I have found some minor issues with the receiver that are already being corrected and should not be an issue on the next prototype receiver.

Back to the rifles performance. As mentioned, when the barrel is cold in this rifle, it shoots AMAZINGLY well, BUT, I found an issue that has made me change direction a bit on my barrel design. Nothing to do with the receiver part of the rifle, just barrel design. As most of you know, my Raptor LRSS has a double recoil lug design, one in the traditional location between the receiver and barrel but is also has another roughly 8" down the barrel shank that is held tight by a threaded lock nut that sandwiches the lug between the barrel shank and the lock nut, similiar to a Savage barrel design. Then the barrel is held down into the stock by two 1/4x28 tpi tapered head bolts that are threaded right to the barrel shank and pillar bedded to the stock. The receiver is also pillar bedded.

Well, as reported, the rifle would shoot amazing for the first three shot groups out of a cold bore, BUT, the more the rifle was shot, I was getting some vertical stringing down range. This really got apparent at around 1200 yards and out. From a cold barrel, vertical variation was no different then horizontal, around 1/3 moa and usually less then 1/2 moa in the best shooting conditions.

However, when the barrel got warm, horizontal variation stayed the same but vertical variation increased to anywhere from 1 to 1.5 moa!!!!! At first I thought something with the optical system worked loose so checked everything, shot the rifle again, first three shots, well under 1/2 moa, next three over 1 moa......

Set on this problem for a couple days, talked to some good friends for their opinion and told them my theory which I want to share with everyone here as well. To my thinking, and why I did not think of this before is beyond me. Sometimes we have to be slapped in the face to see something.

But, when a barrel warms up, it expands, not only in diameter but also in length. A barrel will stay relatively cool from the throat back because the brass case insulates much of the heat away from the barrel. From the throat down to the muzzle, the barrel will heat up, most of this heat is in the first 1/2 of the length of the barrel. As such, this will be the portion of barrel that grows the most in length as it heats up.

This brings us to my problem. With the double recoil lugs beddes solidly front and back, there is no room for the barrel expansion to go and in my theory, you will get a bowing of the barrel as it heats up. The barrel shank will grow slightly in length, causing the rear recoil lug to push hard on its rearward surface and also causing the forward recoil lug to push solidly against its forward surface. When the two contact, the barrel will flex causing vertical variation as the barrel heats up as the muzzle will be flexed in slightly different locations as the barrel warms more and more.

I tested this to see if I was on the right path. Shot three shots with great accuracy, then followed quickly by another three shots, this time easily three times larger in group from vertical variation.

let the barrel cool completely and retested, first three shots again shoot EXTREMELY tight, well under 1/2 moa, the next three over 1 moa.

Let the barrel cool again, just to make sure I could repeat what was happening consistantly and it did exactly the same thing again.

So, I headed back to the shop, pulled the barreled receiver, removed the lock nut and recoil lug, machined a simple .250" stainless steel spacer ring to take up the room of the recoil lug between the lock nut and barrel and reassembled the rifle with no other changes and headed back to the range.

Using the same exact ammo throught testing. This time, the rifle shoot very well for the first three and the second three strings. It took twice as many rounds but after that there was still some slight vertical variation. Not nearly as much as before, in fact I had to shoot several groups on video to be able to really tell a consistant pattern but there was obviously more vertical variation then horizontal. Many would say that could just be velocity spreads or BC variations or something like that but in every case, from a cold barrel, the first three shots always had the same or less vertical variation compared to horizontal variation.

I headed back to the shop.

Over the next couple days I thought about the problem more and decided to remove the forward barrel mounting screw which was positioned roughly 1" behind the forward recoil lug. I also decided to mill the stock so that the barrel would be free floated for most of the barrel shank. I did however leave the rear barrel mounting screw which is positioned roughly right at the location of the chamber neck on the barrel, around 1.750" ahead of the conventional recoil lug position.

My theory here was that this section of barrel would expand in length very little if any because that section of barrel would not heat up much. From that point out would be the main barrel expansion so that is why I floated the barrel from there out.

First and only outing with that change proved VERY good results. In fact, I hate to say this but I heated the barrel up pretty good on several occasions and could not see a real distinct increase in vertical variation. As such, I believe that there is no point to the Double recoil lug design because of the barrel length expansion as the barrel heats up. In a small, low intensity chambering such as many of the conventional BR class chamberings, barrel heat may be low enough that this would never be a problem with a barrel of this mass but with a 338 AX eating up 100-110 grains of powder on each shot, just not viable.

I have only been able to get the rifle back out to the range that one time but plan on doing much more testing. I also contacted Dan Lilja and sent him a new barrel contour drawing for him to make for me for the LRSS rifles. Basically, it will be the same barrel, 1.350" full diameter shank for 8" but with the new barrel, it will contour down to roughly a #8 Lilja contour from there out. Barrel will still be fluted on shank and down the tapered section of the barrel. I plan to still retain the single barrel mounting screw under the shoulder/neck location and will bed the barrel 1" ahead of that point but will free float the barrel from there out.

The good news is that this will reduce the labor and hardware in making the rifles and should drop around $200-$250 off the price of each Raptor LRSS. Thats always a good thing!!!

Today at lunch I also did some load development with the 225 gr Accubond. On our field test hunt in Oklahoma, I was a bit less then impressed with the performance of the 300 gr SMK when used on lighter game such as lighter deer and sheep. In the heavy Aoudad it worked noticably better and it works very well on even heavier game but on the lighter game, it seemed the bullet was the majority of the way through the animal before it started to expand. As such, I wanted to test a lighter bullet that is known for good expansion performance.

I remembered that Goodgrouper had had very good results with the 225 gr Accubond in his 338 Thunder loaded to around 3300 fps so I wanted to see what my 338 AX would spit them out at. I started at 105.0 gr Retumbo with a 3.685" OAL which is seated JUST to touch the origins of the hybrid throat. It was very windy today so I only did 100 yard shooting for chrono data more then anything but the bullet did shoot several 1/2 moa three shot groups.

105.0 gr................................3305 fps
106.0 gr................................3334 fps
107.0 gr................................3385 fps
108.0 gr................................3400 fps 100% load density
109.0 gr................................3436 fps
110.0 gr................................3471 fps A bit more powder crunching then I like

Even at 110.0 gr, chamber pressure was less then the load I am using with my 300 gr SMK load at 3000 fps. I know this because I made a special tool to check for case head expansion. Basically, a virgin Lapua case head will slip into this guage but its such a quality fit that if there is any head expansion at all on the case extraction groove, it will not slide into this guage. Its similiar to a shellholder in design.

My 300 gr SMK, 3000 fps loads will slip into this guage with some minor pressure needed. The 110 gr load with the 225 gr Accubond falls in and out with no pressure at all. Still, I do not like crunching powder as much as the 110 gr load was so I dropped down to 109.0 gr and shot five shots over several minutes to get a velocity string. Those numbers were:

3431, 3436, 3433, 3435 and 3433 fps. I was pretty impressed by that. Those five shots also carved a ragged hole at 100 yards as well so I will be testing that load at long range. I am giving up a quite a bit of BC over the 300 gr SMK but also gaining nearly 500 fps of velocity as well.

The best thing, the Raptor barely twitches when it spits these bullets out compared to the 300 gr SMK, I was most suprised at the difference in felt recoil. Will be fun to try these at long range.

I also was curious to check the drop and drift numbers compared to my 300 gr SMK load just to see how the lighter bullet would compare. I have always been a fan of a higher BC bullet at moderate velocity but for lighter game, I want to give these bullets a chance to see if their terminal impact effect is more impressive on lighter game. Here are some drift and drop numbers, both with 100 yard zeros, 10 mph crosswind:

Yards..................225 gr AB(drop/drift)..................300 gr SMK(drop/drift)
500.....................-30.5"/11"..................................-39.8"/9.1"
750.....................-88.5"/26.3"...............................-110.1"/21/6"
1000...................-188.3"/50.1".............................-225.3"/40.6"
1250...................-344.8"/84.5".............................-396.3"/67.0
1500...................-579.6"/131.9"...........................-637.7"/102.4"
1750...................-923.5"/194.8"...........................-968.8"/148.1"
2000...................-1417"/-273.6"..........................-1415"/-205.6"

I like to maintain 1500 fps for adiquate bullet performance. Now the Accubond will likely expand more reliably at 1500 fps then the SMK but that is a value I like. Comparing the two, the 300 gr SMK loaded to 2980 fps will maintain 1500 fps out to roughly 1580 yards at my location. The 225 gr Accubond loaded to 3435 fps will maintain this 1500 fps out to around 1415 yards.

Certainly the 300 gr SMK has a distinct edge in drift performance and sustains velocity to father ranges but to me personally, 1400 yards is a HELL of a long way, most of my big game hunting, even long range hunting will be in the 700 to 1000 yard range and for this range, either bullet would work perfectly well.

Even though the 300 gr SMK will have a higher kenetic energy payload at long range, I believe the 225 Accubond will be more terminally impressive on lighter game because of its ability to transfer energy faster as it will open up much quicker on lighter game.

Please understand that I am not faulting the 300 gr SMK, its a great bullet but it performs similiar to a premium bullet as far as penetration and expansion at long range are concerned, that is great for a 700 lb elk, not so good for a 100 lb pronghorn or 200 lb whitetail at long range. Will it certainly get the job done, you bet but we hammered a fair share of exotic sheep at ranges from 300 to 800 yards and some of the shots did not seem to do the damange they should have with this class of bullet. Just want to see what the Accubond can do. I wish the 250 gr AB had a better BC value, it should really be much higher then .575 when the 225 gr is listed at .550.....

Anyway, second prototype is headed this way for the next Raptor. This one should be a production reciever with all my engraving as it will be on the factory receivers. I will use the new barrel contour and give that a test and if it meets my requirements, we will be very close to ready for taking orders. I hope that happens by April/May of this spring.

Also working hard on the Raptor Stalker with a slimmed down barrel design similiar to the LRSS but much lighter and it will be in a sporter style stock, again, a 9 lb version of the Raptor LRSS instead of 16 lbs. I hope to have the Stalker ready for orders by this summer.

Just wanted to get you an update if anyone was interested and curious to the results of the R&D stages of the Raptor rifle systems. Take care and good shooting.
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Old 02-23-2010, 03:47 PM
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Re: Raptor LRSS progress report....

Good report Kirby. Have you thought about using the 250grn Hornady HPBT? The one guy trying to hit a piece of plywood at 2285 could only do it with that bullet. With a BC of .675 at your velocities should be quite impressive at long range and with good terminal performance. One smith I know switched from 168SMK's in his 300WM because they would not reliably open. He switched to the Hornady 168 HPBT and he said the problem went away. Just a thought.

Tank
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Old 02-23-2010, 05:01 PM
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Re: Raptor LRSS progress report....

Your post reminds me of an earlier post I read by NesikaChad. He stated that he'd never seen a competition rifle with more than one recoil lug, and that more than one lug seemed to be a no-no, without explaining why. I think he was mostly just commenting on his observations than trying to explain the rationale for a single recoil lug only design. It sounds like you've identified at least one reason to stay away from dual recoil lugs. Thanks for sharing your findings and the updated projection for the Stalker version of your Raptor receiver.
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Old 02-23-2010, 08:50 PM
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Re: Raptor LRSS progress report....

Very nice Kirby, thats how you learn right, try new idea's and than put them to the test. I really think it is great how you tell about things that work and those that do not. No other gunsmith I know of does this, I believe people really like to hear this and not just all great things other gunsmiths talk about.
I commend you sir.

PS: still interested when stalker version comes out make it lighter if possible in a 7mm allen mag or there abouts.
What is time frame if stalker version shows it head when you want?
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Old 02-24-2010, 12:39 PM
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Re: Raptor LRSS progress report....

It's so much fun to be able to read about your "hits and misses" in the development of your Raptor. It makes me feel like I've been part of it. It also instills confidence in those of us that think we would like one of these in the future. We KNOW that it has been wrung out from start to finish. It must also be satisfying from your perspective to identify those things that dont work as well and seeing them resolved as you "fix" the problem. I cant wait to shoot her myself. Now, if we could just get a chinook to clear away some of this snow.............

Jim
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Old 02-24-2010, 01:06 PM
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Re: Raptor LRSS progress report....

Using a video camera during load testing is a whole new world of insight for me. I see things I never noticed while looking through the scope. And best of all I do not have to rely on my memory.

Very interesting that the 225 Accubond stays ahead of the SMK for drop all the way to 2K.
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Old 02-24-2010, 01:39 PM
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Re: Raptor LRSS progress report....

It's always more interesting for me to read about the "good, bad and ugly". Most only tell you about the sunshine but never the rain. That and you go into such detail about what worked and why as well as what didn't work and why. Again, it's refreshing to read about the not so great results instead of everything coming up roses type posts.

Any chance you're going to test the 250 Accubonds? If nothing else just to see what kind of FPS you get compared to the 225's.

For some reason I have it in my head the 250 Accubond should be about the best all around hunting bullet in the big 338's.
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