This is the .50 Bontrager bigbore. It was the first 500 fpe bigbore I ever had, and I really love it, it is my BABY. It's accurate, powerful, and goodlooking. I know it's not a Barnes' he..he..but it's my most favorite airgun in my airgun arsenal. When I firsrt recieved this gun, I was in love with it, I couldn't take my eyes off it for a while due to its look and its immense power. It has plenty of air, 3 full power shots, plus 2 back up shots at around 350 fpe with 3500 psi. I will make it even more powerful by swapping to the more powerful hammer spring and hopefully bring it up to around 650 fpe for 2 shots. I plan to hunt biggames with it in the future, should be a lot of fun.....
P.S Sorry for the pictures, indoor it's always bad lighting plus my camara skill is not to good he..he..I need a real camara instead of the iphone he..he..

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Edited 3 time(s). Last edit at 03/25/2010 09:25AM by peter-n.

Hi Peter,

Very nice. I'm really glad you have it and enjoy it so much. That's what it's all about.

I see, and understand how he's designed the bolt lock up system. It's interesting, and I commend him on providing three lock up points. He's using the head of one machine screw stopping against the edge of the receiver housing (up front). And he's using the shaft of a machine screw stopping against the shoulders of the pierced bolt in the back. I suspect the rear bolt, also is part of the mounting of the top receiver tube to the bottom hammer tube. The bolt is pierced with the groove going clear thru the bolt - and then the pierced groove turns 90 degrees. The forward shoulders of the turned section of the groove provide stop surfaces against the bolt shank.

I think you mentioned (previous post) that there were 3 locks. That would be the two forward edges of the turned sections of the groove, and the head of the machine screw forward. It's that rear bolt that is the critical lock component. That's not just an extra thing to catch the bolt if it were to blow back. That's doing more than 2/3 of the bolt lock up system. The front is the lesser component, by a good bit.

I don't suspect any problems, and I make no judgements. What we do not know, however; are these questions:

1). What's the size and tensile strength of the rear bolt shaft? It should be a very high strength bolt. That would be the width of the groove. Your 051 pic shows it as about 1/3 of the width of the total bolt. That would be .166" Might then be a 3/16" (.187") diameter shaft. That's really providing most of the strength of the system. It has to be of exceptional quality. I suspect that bolt was chosen to present the smooth shaft of a longer bolt, and the theads should only be down inside the lower housing. You should not see thread on the bolt shaft anywhere. Reason being that the threads are grooves across the shaft, which weaken anything being used in a "shear" capicity.

2). What's the size and tensile of the front machine screw? It should be very high tensile as well, as it's the shaft, and not the head, that's the weakest point. You see, the shaft is smaller, and has grooves cut around it, in the form of threads. The way to break a shaft is to cut a groove in it and stress it sideways. So, it's the bottom of the thread groove, that's the thickest (strongest) point of that machine screw. That looks like about a 5/16" diameter head. That would make it a 3/16" shaft machine screw. To tap for a 3/16 machine screw ... you drill about a .159" hole. Therefore, the strongest point of that screw, when it's being used sideways in this application ... is .159" of steel. The head is actually providing leverage against this shaft. Bolts are designed to be strongest in "tension" ... meaning when being pulled end to end. When used in a "shear" application, like this, then the tensile of the steel is critical across that crossection of approx. .159"

So; there ya go. That's the facts as I see them. Finding no fault. I just don't know the answers to the questions named. Not knowing them, I'd make very sure that those two bolts are in pristine condition. (You mentioned one bent at one time ... I hope you replaced it, because high tensile bolts would not bend, and you have to have these components perfect). You must also make sure that the holes it's threaded into are not stretched. We don't know if the bolt is hardened tool steel, or lesser mild steel. Guess that's question #3.

Thanks for sharing the pics of your fine gun Peter. Someone spent alot of time and effort on making that for you. It deserves someone who appreciates it and uses it. You just need to understand it's design. You must maintain it properly. Most of all, you must not ask it to perform tasks the maker did not design it to do.



Gary

You have a very good eye Gary for observing things even through the pictures. You're right about everything you said regarding the bolt locking points and the strengh/weakness of the maching screw heads. That was why I took the closeup shot and knew that you would understand it right away, after all you're a Master airgun builder. His later design on the bolt/receiver lockup is better due to without having to use the machining screws. My only concern is the screws might get weaken or rusted after a period of time and should be replaced. Is my concern valid? I think he had mentioned that the machining screws were heat treated.

You're also right about the amount of works the builder had put into it. Because Joe had mentinoned in an email to me a couple years back that his "real" reward is not really the money but the satisfactions and enjoyment of the customers, he claimed he didn't make that much money on the guns after putting so much time into designing and building them. And I believe him. I've always appreciate the custom guns and think that it's worth every penny and more after realizing how much effort the builders had put into it.

Hello Peter,

I don't think you need to worry about rust or fatigue, "IF" the bolts are correct for their usage. Bolts like that, could be as low as a tensile of around 60,000 psi. For that purpose, I'd use bolts of 190,000 psi tensile. So, if any replacement would be warrented, it would be for tensile strength. The bolts would really look alike. You'd need to know any company markings. Or, best case, just buy the correct thing and know they are right.

You didn't mention. The rear bolt that goes thru the slot. Is that shaft inside the slot, smooth? If it's showing threads, then it wouldn't be ideal. The threads should be on the extreme bottom, inside the housing. You shouldn't see any in the slot. I'm not picking. Just offering the best situation, for the design you've shown.



Gary

Yes Gary, the rear bolt is smooth and has thread on the bottom one third to thread down into the bottom housing like you said.

Peter, that's a fine looking gun. I can tell from the luster of the stock it's been well rubbed by you over the years. It's good to see someone taking the time to share the hobby. Your pics look fine, now for some action "shots" of the Bontrager breaking something.

Kent

Thanks Kent! yes I will take it out shooting/hunting and post some pictures. It would be nice to be able to call in some coyotes and blow them away with it he..he...

I've been thinking of getting a cheap electronic call too. I could sit in the War Wagon and "hunt". haha. I saw a pr. of Foxes not long ago (but they were at 200 yards). I could maybe call them in closer.

Gary