Suppressor rear bush sizing

Looking for some feedback on what the correct sizing (clearance) should be between the barrel and the rear bush on an over barrel suppressor. I have just fitted a DPT suppressor to a Sauer 100. Barrel diameter at the where the rear bush sits is 17.5mm. I had the store I purchased the suppressor from send the bush to DPT with that barrel measurement for the bush to be turned out for the correct clearance. I have just received it back and the bush ID is 17.6mm, so a 0.1 clearance on the barrel. i am wondering if this is sufficient. I also have a Tikka with a DPT suppressor, on this setup the bush to barrel clearance is 0.33mm. This was done a couple of years ago and from memory the bush was turned out for clearance at the shop I purchased it from and not DPT. So the question is which is correct? and more importantly is a 0.1mm clearance sufficient.

Every rifle is different

I have seen them with any amount of clearance and some an interference fit

If load development is done with the suppressor fitted then life is good

Most would prefer clearance rear bush to barrel O/D

I think this is one of those it depends who you ask questions.

The guys at my local gun store reckon there needs to be clearance but you want it to be minimal, so you don't get scrub etc down there while you're out hunting and creating contact between barrel and suppressor.

On the other hand my Hardy suppressor that was fitted by them is rubbing a shiny spot on the barrel and is definitely contacting the barrel. 0.1 should be plenty.

Went through a similar thing after H&F cocked up an order. DPT were very helpful. Talk to them directly.

Recently got dpt to machine a bush for me. Can't remember actual size but it was only 0.1mm clearance.

Needs to be a good clearance, quite often the bore is not concentric to the outside of the barrel, you don't want the bush trying to tip the suppressor.

Thanks for the feedback so far. Yes I do intend to call DPT for their feed back. My concerns was that o.1mm is a tight tolerance and if the threads on the barrel or the suppressor are even a tiny bit off centre then the suppressor could end up contacting the barrel. Or worse still there could be clearance with a cold barrel and contact after the barrel heats up leading to accuracy problems. I thought that the point of the bush was that if the suppressor happened to come loose on the threads then the bush would keep the suppressor centered enough to stop a bullet contacting the baffles and causing damage.

half of my suppressors are firm fit with bush firmly against barrel.....it cant move if its tight,nowhere to go.

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Originally Posted by Micky Duck

half of my suppressors are firm fit with bush firmly against barrel.....it cant move if its tight,nowhere to go.

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Yep I get that. solid consistent contact or no contact at all should work. But partial or variable contact would most likely cause accuracy issues.

Easy way to find out is shoot a string of 5 and see if it walks or effects anything. The Bush can always be machined more if you get inconsistencies as the barrel heats up.

My money is on its fine, go hunting

I don't run any rear bushes, 1 is DPT other is GBC/gun supplies, no issues with stuff falling between barrel and suppressor, accuracy is good.

I vaguely remember DPT saying that the rear bush isn't necessary at all re: noise reduction. Don't quote me on that, I may have misremembered.

Hi,

The rear bush should have 0.05mm clearance, 0.1mm is fine. To confirm its not touching the barrel, firmly screw the suppressor onto the barrel, then unscrew the rear bush, if you feel the bush rubbing the barrel then the bush needs to be made slightly larger, if not then its fine.

The suppressor should have been supplied to you with instructions, the bush clearance is mentioned in there.

Ha, if all else fails read the instructions aye.

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Originally Posted by DPT

Hi,

The rear bush should have 0.05mm clearance, 0.1mm is fine. To confirm its not touching the barrel, firmly screw the suppressor onto the barrel, then unscrew the rear bush, if you feel the bush rubbing the barrel then the bush needs to be made slightly larger, if not then its fine.

The suppressor should have been supplied to you with instructions, the bush clearance is mentioned in there.

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Thanks for that. Yep should have read the instructions. I read them when I purchased my first DPT I remember the maintenance instructions and I follow them, it didn't occur to me the clearnce info woul be in there, my bad. Anyway thanks for the advice I will do that.

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Originally Posted by Bushwalker

I don't run any rear bushes, 1 is DPT other is GBC/gun supplies, no issues with stuff falling between barrel and suppressor, accuracy is good.

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ditto, DPT no rear bush here.

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Originally Posted by vulcannz

ditto, DPT no rear bush here.

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My concern with that approach is that if the suppressor was to come loose on the threads while shooting there is a real rish of bullet contact with the baffles, the end result of that doesn't bear thinking about. Pretty sure this is the reason the bush is there.

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Originally Posted by zeropak

My concern with that approach is that if the suppressor was to come loose on the threads while shooting there is a real rish of bullet contact with the baffles, the end result of that doesn't bear thinking about. Pretty sure this is the reason the bush is there.

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No different to a muzzle forward, heaps of people running them without issue.

The bush serves to protect the mounting thread if the can gets a bash

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Originally Posted by Nick-D

No different to a muzzle forward, heaps of people running them without issue.

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Good point

Me personally prefer a fairly big clearance. I check my silencers regularly to ensure they haven't come loose.

I found my rifles to group better with the rear bush(s) not touching. Then again - I prefer muzzle forward silencers.

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Originally Posted by Fssprecision

Needs to be a good clearance, quite often the bore is not concentric to the outside of the barrel, you don't want the bush trying to tip the suppressor.

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Even though I don't have any over barrel suppressors, but have owned a Savage with a terrible banana barrel.
The bore was straight and either end was concentric, but the middle was wildly off centre.
An armorer told me that this is not unusual even for premier rifles.
So out of curiosity, what do you do when the bush is only touching at one point on the barrel ?

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Originally Posted by Hall

Even though I don't have any over barrel suppressors, but have owned a Savage with a terrible banana barrel.
The bore was straight and either end was concentric, but the middle was wildly off centre.
An armorer told me that this is not unusual even for premier rifles.
So out of curiosity, what do you do when the bush is only touching at one point on the barrel ?

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Relieve it….open it up concentrically till it has clearance ie not touching all round…unskilled opinion….!

Another vote for not running a rear bushing. My DPT on the 7mm08 M7 been fine without it.

The bore is concentric at each end but is frequently eccentric between those points due to barrel straightening after profile turning. When I machine a muzzle I first check the bore for straightness and correct it if needed before turning and threading the muzzle between centres. I then clock the OD of the barrel at the rear bushing point and note any runout. I can then calculate the correct bushing size with a minimum size that will not exert any eccentric pressure. Bushing contact on an eccentric OD can cause accuracy problems, especially as the barrel heats up. A true concentric barrel will shoot better with the bush in contact.

Exactly what I was saying earlier but most on here know best ha ha