jriggs Posted June 2, 2014 Share Posted June 2, 2014 so once i throw in this low mass bolt and buffer/spring....will the POI change at all or will it be pretty much the same. I'm sure it changes muzzle velocity but is it enough to really change POI? thanks in advance, Riggs Link to comment Share on other sites More sharing options...
DocMedic Posted June 2, 2014 Share Posted June 2, 2014 (edited) In theory? No. The same pressure of gas will still push into the gas block, but the gas block is only letting so much gas coming into the gas tube, there for the residual gas will return back into the barrel, and by that time the bullet should had already left. Adjusting the gas block should just changes how the BCG cycles, I believe. Edited June 2, 2014 by DocMedic Link to comment Share on other sites More sharing options...
DocMedic Posted June 2, 2014 Share Posted June 2, 2014 (edited) Now that I think about it. If its the same gasblock thats been on the rifle and you're just adjusting it then I would think you wouldn't see a change in POI, HOWEVER if you put on a NEW Gasblock that is adjustable and replacing one that wasn't then yes it would change your POI based on barrel harmonics. Edited June 2, 2014 by DocMedic Link to comment Share on other sites More sharing options...
jriggs Posted June 2, 2014 Author Share Posted June 2, 2014 Same JP adjustable gas block... Just swapping out a full mass carrier for a boomfab unit and a different buffer/spring. Link to comment Share on other sites More sharing options...
polymerfeelsweirdman Posted June 3, 2014 Share Posted June 3, 2014 (edited) I don't think velocity will change much, partly because the seal between the gas block and barrel typically isn't perfect anyways, and POI will change but it will be negligible and dependent on the gas system. Just my educated guesses which could be completely wrong as mechanics is not my specialty. Edited June 3, 2014 by polymerfeelsweirdman Link to comment Share on other sites More sharing options...
openclassterror Posted June 3, 2014 Share Posted June 3, 2014 Very minor changes in harmonics can have a significant effect on both group size and location. They can also have very little. The Browning BOSS adjustable brake has no effect on velocity at all, but adjusting it 1/4 turn can change group size by ( in my experience) as much as 40%, as well as relocate the group center by 3/4" at 100 yd. At other spots in its rotation, a half turn makes no difference at all. Only way to know is to shoot it before and after against a known zero and adjust if necessary. The gas tube acts a little like a tuning fork and absorbs some of the barrel vibration, which is one reason why the AR has potential to be very accurate. But saying it will or won't is very much a case by case thing. Link to comment Share on other sites More sharing options...
jriggs Posted June 3, 2014 Author Share Posted June 3, 2014 Thanks terror, I was pretty sure it would make a difference but was just curious as to how much. Wednesday all the parts arrive and I'm going back and forth about whether or not to toss them in and adjust the gas and the zero because I have a comp on Saturday to go shoot. I'm leaning towards not doing it because what I have runs and I'll only have 150-200 test rounds on the rifle before the comp and that's not a lot. But it's like Christmas and I want to play with my new toys! Link to comment Share on other sites More sharing options...
openclassterror Posted June 3, 2014 Share Posted June 3, 2014 I have the same quandary just about every match. I love messing with my stuff, and rarely run the same setup on two consecutive matches. My rule of thumb- Local match, I will dink around 'til the last minute- even if it means sighting in the morning of the match. Because it REALLY doesn't matter how I place. Bigger matches, I won't mess with anything within a week. Except this week I'm taking an untested big-chassis AR to Ironman, and I will be working up loads tomorrow. Also changing bullet weights on my little gun, because the throat is gone and I am hoping to regain some accuracy with a heavier bullet. Come to think of it, I'm SCREWED!!! Tom Link to comment Share on other sites More sharing options...
Stlhead Posted June 3, 2014 Share Posted June 3, 2014 I have never seen adjusting an existing gas block effect my group size or relative zero. Not saying it couldn't happen, just that I have not seen it. I would still confirm zero before a match anyway, so even if it did it would not matter. You will be shooting the gun to adjust the gas anyway, why not do it at a target. Link to comment Share on other sites More sharing options...
openclassterror Posted June 3, 2014 Share Posted June 3, 2014 To be a little clearer, I don't know that just making a small gas adjustment would make very much difference, but he is talking about changing the buffer and carrier as well. Which usually means a fairly significant gas adjustment, as well as a weight change. When setting up the adjustable gas block on my LR308 last Friday, I did notice that going from closed gas block to enough gas for bolt lock, POI went about 2" left at 300 yds. Not huge, but enough to see. Granted, that was no gas to full gas. But it definitely caused a group center shift, unless there was another factor I was not accounting for. Link to comment Share on other sites More sharing options...
Stlhead Posted June 3, 2014 Share Posted June 3, 2014 Changing a buffer and bolt carrier will certainly change the zero, but the original question was if adjusting the gas would move his zero. Link to comment Share on other sites More sharing options...
jriggs Posted June 3, 2014 Author Share Posted June 3, 2014 ok i'll be setting up targets at 200 and 300 to re-zero. yes I'm swapping out a mil spec full mass carrier for a boomfab unit and also throwing a JP low mass rifle buffer and spring in there also...so it's going to be A LOT less gas and a totally different set of guts inside the gun. Link to comment Share on other sites More sharing options...
Mberry Posted June 3, 2014 Share Posted June 3, 2014 Please post your results. I don't think it will change much, if any. Link to comment Share on other sites More sharing options...
jriggs Posted June 4, 2014 Author Share Posted June 4, 2014 Will do... Link to comment Share on other sites More sharing options...
tortuga Posted June 4, 2014 Share Posted June 4, 2014 This is an interesting topic for me, as a old-school bolt action varmint / target shooter learning about the AR platform. For what it is worth, I think anything that changes the recoil characteristics of the rifle/pistol/whatever changes the POI. The rig is moving before the bullet leaves the barrel; where it is when the bullet leaves the barrel matters. I can't see how any change that significantly affects the recoil can not affect the POI. I sighted in a pistol for a state NRA Hunter Pistol match with a bipod on the forearm, and took it off for the match. POI shifted enough to make it a wasted trip. Got some good groups, though. Anyway, I'm still trying to figure out why nobody worries about headspace, action truing, neck sizing, brass sorting, stock bedding, and all the other crap we varmint hunters tinker with. Link to comment Share on other sites More sharing options...
DocMedic Posted June 4, 2014 Share Posted June 4, 2014 (edited) For what it is worth, I think anything that changes the recoil characteristics of the rifle/pistol/whatever changes the POI. The rig is moving before the bullet leaves the barrel; where it is when the bullet leaves the barrel matters. I can't see how any change that significantly affects the recoil can not affect the POI. Anyway, I'm still trying to figure out why nobody worries about headspace, action truing, neck sizing, brass sorting, stock bedding, and all the other crap we varmint hunters tinker with. I'm not a Firearms Engineer but from what I've seen in documents, The bullet leaves a AR well before anything mechanical starts moving (ie. BCG unlocking and receiving the next round.) The reason we as AR shooters have to focus on follow through has more to do with Trigger lock time. (the time it takes the pull of the trigger for the hammer to hit the firing pin.) On a bolt gun trigger lock time is about x3 faster then it is on the best triggers for AR's. again where only talking about Millionths of seconds but that's the difference between a hit on a 2inch plate at 100 yards. For Headspacing I don't think it relevant since at least people in these forums usually buy high quality barrels. Technology has improved so much for AR barrel making process that the Manufactures can adjust for any deviations such as thermal expansion, that they can still hold a trued .0001 of a inch headspace Action truing? I believe thats one of those things that isn't worth the benefit for the effort, plus I'm not sure how you would true a bolt that is 8lug'd(?) since its a rough Sandwich process to get the next round into the shooting chamber. Stock bedding? dont need it, AR's are Chassis systems and higher quality rifles are free float. As for shorting brass, neck tuning etc? There are still people who do this, hell I've known people that will weigh each bullet before they load it. You'll still see this for NRA highpower events, as they're trying to squeeze every piece of accuracy they can get to get those "X"s. In action shooting sports being able to hit a 4 inch target at 100yards is all we need. If your doing all of this for Action shooting sports.. well you have more free time then I do Edited June 4, 2014 by DocMedic Link to comment Share on other sites More sharing options...
jriggs Posted June 4, 2014 Author Share Posted June 4, 2014 (edited) so just before lunch the UPS guy stopped by and gave me a box from JP and a box from BOOMFAB. so I went to my place which is about 5 miles away and played around. first target is the standard mil spec full mass carrier with standard rifle buffer/spring. I shot a 10 shot group of the hood of the trunk of my car at 100 yards. (NOTE: group was a little left which was odd..i looked down and was one click left for windage for some reason, so I reset to zero) so then I closed the gas system down and pulled out the carrier and buffer/spring. I swapped out the carrier parts onto the BOOMFAB and put it and the low mass buffer/spring from JP in the rifle. I was 4.75 turns out for standard mass...and 3.75 out for the boomfab. so I got one whole turn down in gas for reliable cycle. not sure if the buffer spring breaks in or not but i'll play with it as I get more rounds on the rifle. second target is the boomfab carrier and JP buffer/spring. once again off the trunk of the car...group is a little less tight but I was running around with the dogs while I let the rifle cool off a bit...so I was a little shaky group is a little right but don't forget I made the correction for windage that somehow got onto my scope. seems like no change or little change. I'm sure if I had bagged the rifle up on a bench and taken more time there may have been a slight adjustment...but like stated above...only a benchy would care about that. love the unit...it's a nicely made carrier....looks really cool. there is a noticeable lack of push on my shoulder and regardless of whether or not is makes me faster..i feel faster HAHA NOTE: in the box was a JP cleaning guide....I think that was the most impressive piece of gear in the box...that guide is a thing of beauty and I'm gonna feel bad getting it dirty Edited June 4, 2014 by jriggs Link to comment Share on other sites More sharing options...
Mberry Posted June 4, 2014 Share Posted June 4, 2014 Looks good! Good luck at York. Nice spotting scope too! You have excellent taste. Link to comment Share on other sites More sharing options...
jriggs Posted June 4, 2014 Author Share Posted June 4, 2014 Thanks Mark! good luck to you too...this weekend is the Noveske shoot..isn't it? yeah that spotter has been through hell up in the mountains in WY...and when you're glassing for 8-10 hours a day....it makes a BIG difference having good glass. it can be a little heavy when paired with my favorite tripod...but who cares when you're up in the mountains! Link to comment Share on other sites More sharing options...
Jadeslade Posted June 4, 2014 Share Posted June 4, 2014 Did you chrono it? How much velocity is lost? Link to comment Share on other sites More sharing options...
jriggs Posted June 4, 2014 Author Share Posted June 4, 2014 Nope. Didn't break out the chrono. Link to comment Share on other sites More sharing options...
jriggs Posted June 4, 2014 Author Share Posted June 4, 2014 (edited) http://youtu.be/IHgcKgthQuMI do this a lot...just sit up on the hill and shoot at my steel targets at 300 yards..and I i can say there is a noticeable difference to me for sure when sending a round and getting back on target...the scope didn't move much and settling the reticle was smooth and easy. Edited June 5, 2014 by jriggs Link to comment Share on other sites More sharing options...
tortuga Posted June 5, 2014 Share Posted June 5, 2014 You had 7 above the center dot with one, 7 below with the other. I would say the POI changed. Link to comment Share on other sites More sharing options...
jriggs Posted June 5, 2014 Author Share Posted June 5, 2014 (edited) Yeah like I said.....either no change or very little change due to some testing that was a little rough and not very precise. But yeah....there could be a solid 1" in elevation there when you look at the groups Edited June 5, 2014 by jriggs Link to comment Share on other sites More sharing options...
Mthomas0001 Posted June 11, 2014 Share Posted June 11, 2014 Great info - thanks guys!! Link to comment Share on other sites More sharing options...
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