|
||||||||||||||||||||||||||||||||||||||
Industry Professional
One of the lugs broke on my Model 1 Sales bolt at around 5000 rounds last month. That's pretty good for a bottom-of-the-line part. Coincidentally, I rebuilt the upper with a 16" Noveske barrel and CMT parts a couple of weeks ago. We'll see how long the bolt lasts this time. I bet I get to 10,000 rounds this time (if I can afford it...).
Stephen
SENIOR STAFF
I think that will be 99.99% of civilian issues rather than breaking a bolt.Originally Posted by Stephen_ATS
Member
The reason that I went with 6.8 is because I wanted a harder hitting cartridge out of a 10.5" barrel. I had serious issues with 5.56 out of that length barrel in Iraq using M855. So my choices were to shoot Mk262 and get about 100-120 yards of fragmentation range (depending on who you ask, I have my own doubts), or go with 6.5 Grendel or 6.8 SPC and do my own research to find it's performance data. Based on ammo costs, all three rounds (Mk262, 6.5G, and 6.8SPC) were all about the same, but based on initial research, both the 6.5G and the 6.8SPC would outperform the bigger 5.56. So, the choices were 6.8SPC or 6.5G. The reason that I chose 6.8 over the 6.5 is because of two reasons:
1. 6.8 uses a stronger bolt than the Grendel
2. 6.8 is produced by more than one company (competition is good)
The 5.56 would be a good idea for a limited budget as you could just buy military surplus ammo to practice with and then buy some heavy rounds for SHTF.
Through the testing that I've done, I've only shot around 1,000 -1,200 rounds of various manufacture, so I can't tell you about bolt failure....yet.The longest shot that I have taken was 225 yards, but the SSA SMK round fragmented like crazy at that range, so I'm surely happy with the terminal ballistics. I haven't had much more time to do further research, but I think that the Hornady loaded V-max would have much more frag range than that. As far as accuracy goes, I consistently will go sub MOA with SSA SMK's and close to it with Hornady V-max's. I'm very happy with the round and encourage you to try it if it will fit your needs, however it's not for everyone.
Member
Shark, you probably just misworded this and didn't mean to make such an unsupported and erroneous statement, as it would first appear. You probably meant to say that you're guessing the 6.8 bolt is "stronger" because its case head diameter is slightly smaller than 65G's.
Unless you meant it exactly the way you wrote it? In which case I think it would only be fair to present some sort of technical-level proof to back up that statement.
Having said that, Alexander Arms' Beowulf and Grendel bolts (the same unit is used for both) are not your run-of-the-mill 7.62x39 bolt, but have certain engineering details in materials and design that improve their function with those cartridges.
John
Member
Roger that, I meant that the boltface had more material on it than the Grendel Boltface, and that if the two bolts were made out of the same material or had whatever designs to improve durability built into them that the 6.8 bolt would always be stronger due to the extra material, was I wrong? What features are you talking about? I wasn't meaning to bash the Grendel, far from it, and in another thread about 6.8 I mentioned that the Grendel is certaintly the way to go if you need a long distance cartridge to shoot an AR at long distance. Hell, I'll probably buy a 24" upper if wolf ever gets it's ammo to the market. But I do think that the cartridges are not for everybody and neither is a fix-all-do-all cartridge. But based on my needs, I felt that the 6.8 would serve me better. I was just responding to his thread about why I chose 6.8 SPC and why. If any of my information is incorrect, it won't be the first time or last time, but it made sense to me.
PS What did you do exactly to strengthen the bolt? Did you put relief cuts in the lugs like LW did to stiffen them? What material did you make them out of? Are they still compatible with 7.62x39? If they are, you and R. Knight II need to get together and sell about a million AR47's to the military
Industry Professional
Be very careful of what looks to be obvious when you are dealing with fatigue analysis, especially in complex geometry items like a bolt head. To try and give an example that is easier to understand, let's take two steel bars and mount them as a cantilevers with a reversing loading on the free end. One bar is now set up with a crack running 1/3 of the way through, while the other has a nice smooth semi circle cut out of it to a depth of 1/3, the same as the crack. The bar with the semi circle of material removed has significantly less material left in it, so which one is going to fail first.
If I might offer appologies at this stage, I am not going to profer the design details of my bolts over the internet, and you must sympathize with me that I find more than a little amusement in seeing the discusion of the 6.8 suffering from simple but critical design oversights Suffice to say the Beowulf/Grendel bolt design has proven itself historically in close to 9000 units over a 5 nearly 6 year time period. While some are low round count units I also have fielded units where the usage rate will rapidly exceed what is expected from a normal weapon.
I think this thread is not an appropriate place to enter a 6.? discussion, especially as this subject has been somewhat beaten to death. The original question was "Why did, or will you choose the 6.8"
Bill Alexander
Last edited by Bill Alexander; 10-03-06 at 20:48.
Member
I agree and I was just explaining why I went with 6.8, I only mentioned the 6.5 to explain my thought process. I thought that I had a legitimate point on the bolt issue, but I guess that you made relief cuts in the lugs or something else to strengthen them unless you made them out of some sort of unobtanium
1. In an extremely short 10.5-12.0 inch barreled CQB gun, the 6.8 would probably serve you best in that rifle's designed use of 100-200yds.
2. In a full size 20-24 inch barreled sniper or DMR rifle, the 6.5 would win hands down past 100yds.
I won't touch the debate about any other barrel lengths as I don't think that this is the place and it has been hashed out elsewhere, the point of this post is to clarify what I posted earlier in that neither will serve the best in every role and that the original poster should consider what type of platform serves his needs best. At either extreme the answer is obvious and pretty much undebated. I thought that if the guy was looking for a long distance shooter that there was a better option for him that he should know about before committing to the 6.8SPC as the velocity gains from a 16" to 20" SPC barrel are about 50fps.
Mr. Alexander I promise you that I hold you and your design in the highest regards and by no means am I questioning either. But I really would like to know more about your bolt and if you have plans on selling them seperately. Sorry if I came across the wrong way.
Another reason that I went with 6.8 that I didn't mention was that the increased bore size would give the powder more space to burn, thus increasing efficiency out of a 10.5" barrel.
Senior Staff
I think this would be a good time to interject our one main focus here at M4Carbine.net:
We want to deal with accurate information. Not suppositions. Not guesses. Not hypothesis creation for the sake of disparaging gear we didn't choose to buy.
In short, if you have firsthand knowledge of a problem. We would love to hear about it.
If you are quoting material that is EASILY backed up by sources who are credible, for the sake of furthering a discussion, we welcome it.
If you are going to post unsubstantiated opinions, they should NEVER create a reason for someone like Bill Alexander, John Noveske, Mark LaRue, or anyone else to have to come here and defend their products or designs.
We all have opinions on gear, and some of them are backed up by real data. Some are not. We are not going to deal with the ones that aren't.
Member
"Strengthened" 6.8 bolt for those interested in what exactly has been attempted to strengthen a bolt in the past by others. I believe that they use a different material as well versus a standard AR bolt.
Senior Staff
The bolt design you see there was spec'ed for use in the Leitner-Wise .499. Which had suffered from accordian bolts, lug shearing, and other bolt maladies.
They carried over the design features to their 6.8SPC and 5.56N bolts.
I am nearly certain, 99.8%, that design was not brought to market for the 6.8SPC.
Posting Permissions
Reply With Quote
Bookmarks