moderator bore (hole) size

[Miki]

Hi all.

Am looking to identify the diameter of the hole through a calibre specific moderator. For example I have a DPT here in .30 and 25 cal.
The 30cal is 9mm Diam and the 25cal 7.8mm

My 25.06 rounds are 6.5mm so I have a 0.65MM clearance (which seems quite large ?)
The 30 cal bullet is 7.82mm which has a 0.58mm clearance - so this is relatively consistent with DPT.

What size are yours ??

 

[Onelesscharlie]

Most moderators use a bore of at least 1mm over calibre, however .65mm is around the optimum.
Also more and more projectiles have the tendency to yaw on exit from the muzzle, this can lead to the head "kissing" the bore of the moderator, as such some manufacturers are increasing clearance to compensate.

 

[lochty]

I have a Lawrence aurora titanium one, marked .308. Used it for years on my .243, still works fine when I rebarreled to a 7mm 08. It was a bit noisier with the .243 though

 

[Colonel]

I have a T8 mod that is 30cal that I use on my 270 and 223, when I had a 243 with the same thread I used it on that as well it worked well.

 

[wraith]

try and get a mod with a hole as close to the bore size its less loud the more gass you trap the less bang up front my 7mmrem mag with a t8 produses less noise than my 243 with the same mod

 

[Miki]

I was kinda hoping that you guys would measure the hole and post the results here, Whats the size in your T8, 30cal Colonel ??

 

[mealiejimmy]

I have 2 DPT calibre specific moderators
The 22calibre (for my 22-250) has a hole measuring 6.7mm (0.263")
The 6mm calibre (for my 243) has a hole measuring 7.3mm (0.287")

So, it looks like they make the holes approx 1mm (0.040") bigger than the nominal bullet diameter

Cheers

Bruce

 

[FGYT]

Hole size is Bullet Diameter (actual not calibre) plus 1mm to be on the safe side

 

[AN DU RU FOX]

My s5 .25 mod i use on my 6.5 is 7,50mm, and the .30 atec cmm4 is 8.50mm.

 

[Miki]

My 17mod (make unknown) has a 5.2mm bore (which is a 0.35mm clearance)

View attachment 78617

 

[FGYT]

My s5 .25 mod i use on my 6.5 is 7,50mm, and the .30 atec cmm4 is 8.50mm.

I used a .25cal MOD with a 7.5mm hole on my 6.5mm but 6.5mm bullets are actually 6.7mm diameter and it took the MOD off as it yawed thru the MOD bouncing off the baffels (140gn SGK) .

 

[Miki]

I used a .25cal MOD with a 7.5mm hole on my 6.5mm but 6.5mm bullets are actually 6.7mm diameter and it took the MOD off as it yawed thru the MOD bouncing off the baffels (140gn SGK) .

Holy cow, I bet that made your eyes water...

 

[AN DU RU FOX]

I used a .25cal MOD with a 7.5mm hole on my 6.5mm but 6.5mm bullets are actually 6.7mm diameter and it took the MOD off as it yawed thru the MOD bouncing off the baffels (140gn SGK) .

I know thats what i was worried about but an email to ase when i got it and they said the s5 is perfectly safe for the 6,5 as its actually 2mm over if i remember right,i deleted the email off my attachments last year,

 

[Border]

The Hauskens are calibre + 1mm.

 

[FGYT]

I know thats what i was worried about but an email to ase when i got it and they said the s5 is perfectly safe for the 6,5 as its actually 2mm over if i remember right,i deleted the email off my attachments last year,

Yes some .25" mods are fine for 6.5mm as they are made for the cal but badged .25"

Some arnt
Lucky the one I had was a prototype and they had taken the bullet size as 6.5mm now they know and the production ones work perfect.

Even the magneto bayonet chrono attached was fine bar a scratch or 2 after bouncing 20yards down range on concrete

 

[AN DU RU FOX]

 

[bewsher500]

DPT bore sizes

20 CAL- 0,256" - 6.50mm
22 CAL- 0,270" - 6.85mm
6 MM- 0.290" - 7.36mm
6.5 MM- 0.303" - 7.69mm
7 MM - 0.377" - 9.57mm
30 CAL- 0.340" - 8.64mm

I personally run a ".22" DPT on my 6mm BR (a 0.425 radial clearance) I should have gone for the .20 version as its a better match IMO

I also ran a PES T12 Scout "223" mod on my .243 it had a 6.5mm bore (0.25mm radial clearance)

I use a muzzle brake on my 300wm with an 8mm bore (0.19mm radial clearance)
208gr Amax with a bullet length of 1.5"
works like a charm, no yaw

In my opinion the most effective moderators are those that have a 0.25mm or less radial clearance.

If the bullet is yawing enough to move 0.4mm off its radial axis in the first 4" of flight I would have to ask questions around the load, the bullet and the moderator fit
a 6.7 through a 7.5mm hole is more than enough (0.4mm radial clearance


ALL of these closer fit mods and brakes require attention to detail when threading! and you run them at your own risk
use a drill bit of the appropriate size to test if you dont have a decent set of calipers
measure your bullets not just what is stamped on the barrel (.270 is .277, 6.5 is actually 6.72mm etc etc)

Manufacturers will always make mods with higher margin for error as they have no control on fitting and thread tolerance

 

[Nobleman]

So working with the above DPT Bore sizes you could use a 6.7 size bullet through the 6mm mod and still be ok ? I suppose you would invalidate the guarantee or warranty should you do so but it would save buying a specific mod for each calibre.

 

[bewsher500]

So working with the above DPT Bore sizes you could use a 6.7 size bullet through the 6mm mod and still be ok ? I suppose you would invalidate the guarantee or warranty should you do so but it would save buying a specific mod for each calibre.

plenty room assuming the measurements are accurate
not sure any moderator warranty would cover bullets clipping barrels even when correctly installed!

 

[Miki]

DPT bore sizes
20 CAL- 0,256" - 6.50mm
22 CAL- 0,270" - 6.85mm
6 MM- 0.290" - 7.36mm
6.5 MM- 0.303" - 7.69mm
7 MM - 0.377" - 9.57mm
30 CAL- 0.340" - 8.64mm
<with snippage>
In my opinion the most effective moderators are those that have a 0.25mm or less radial clearance.
If the bullet is yawing enough to move 0.4mm off its radial axis in the first 4" of flight I would have to ask questions around the load, the bullet and the moderator fit
a 6.7 through a 7.5mm hole is more than enough (0.4mm radial clearance
Manufacturers will always make mods with higher margin for error as they have no control on fitting and thread tolerance

I spoke with Darren of DPT who tells me that <q> "most of our suppressors are 1.2mm bigger than the projectile size. where the diameter of a 6mm projectile is (actually) 6.2mm our exit hole is 7.4mm. (and) Yes our thread to bore is in perfect alignment".</>
He's a Kiwi, who tend to be a bit American in their outlook, so we have to let him off for rounding up - despite me asking for 'accurate measurements'.

I started this thread as I got into bother with the Lady of the Manor on the estate I shoot. "That's awfully loud" she said of my 25.06 "can't you put a silencer on it ?" - i've got one it's a DPT in 6.5cal with an additional 30cal stainless 1st and 2nd baffle (6 + reflex chamber). It is loaud, I can also see muzzle flash too which is what started me on the bore size question. I have to agree with Bewsher500 in that yaw shouldn't be a problem. My Shultz & Larsen has a pretty well engineered barrel and i'm confident that the threads are very close to the rifles bore.

I'm going to order a set of 6mm baffles from DPT (Bill) for the 25.06. My PPU bullets (100gr) are 6.54mm with my callipers and am confident that the 4.1mm radial clearance will be OK.

Darren follwed your 'margin of error' logic/reasoning (Bewsher500) almost to the letter.