Air Gun Home :: View topic

i8dirt · New Member

Hello,

I am designing a breech for a Crosman 1377 & 2289.

I can't find any drawings for the so called 11mm dovetail standard. Or more specifically I have found conflicting info... 60 degree and 63 degree angle, 11mm at top edge, 11mm in middle of dovetail. How high is the dovetail...

What do the high end European guns measure to?

Any help much appreciated.
Mark

AirGunEric · Site Admin

Why go with the oddball 11mm dovetail? It is far less common that the 3/8" dovetail or a Weaver-style.

I think you would have a much more marketable breech if you went with the Weaver-style rail- Crosman already has a 3/8" dovetail, the 11mm is not as common and getting mounts to fit it can sometimes be an issue.

i8dirt · New Member

Eric,

Thanks for the reply. I know the Picatinny/Weaver mount is "better", but I am after the simple clean non tactical bling look of a dovetail.

If a 3/8" dovetail is more common, I may use that... If I could find the true standard specs for that one also. There is a million adapters and rings for sale but no hard dimension numbers I can find.

Anyone?

Thanks,
Mark

Alstone · Moderator & Site Supporter

I have just checked the rail on my Air Arms TX200 and it is 11mm wide, 1mm high to the edge and 60* deg, most uk quality airguns have 11mm rails?

Al

donec · Senior Member

The difference between (11mm or 0.433inch) and (9.525mm or 0.375inch or 3/8inch) is very small less than 0.058mm or 6 hundredths of an inch. This means for most practical purposes you can use a 3/8 inch mount on an 11mm dovetail since the screws will allow it to open enough. However if you have an 11mm mount and try to attach it to a 3/8inch dovetail it may not tighten enough to hold well as the mount is larger than the dovetail. For this reason I would think that an 11mm would be more compatible than a 3/8inch dovetail.

AirGunEric · Site Admin

Many of the European-made rifles use an 11mm dovetail- that doesn't make it any easier to find mounts easily across the ocean. If the idea is a dovetail, I think you would do better to keep it at 3/8" for a Crosman- no need to cause confusion with customers/potential customers for no good reason.

rsterne · Moderator

FWIW.... A Crosman breech with a Weaver mounting rail might have a built in market.... for those with Red-Dots in particular.... 90% of them either come with Weaver rings or have a built in Weaver mount.... and those that ARE available with a 3/8" mount are ALSO available in Weaver.... Wink

Bob

i8dirt · New Member

Just a quick clarification... I am not going into business making these so I am not going to worry about maintaining the broadest appeal. I just want something a bit different and arguably better (for me) than a crosman breech. Also in the distant future I want to make a "tall" breech to be able to experiment with dampening of the barrel ringing, but first things first. Dimensions of a 3/8 dovetail...

I do not have an example to measure, but is a 3/8" dovetail... 3/8 at the outermost edge, 60 degrees and .09" tall?

Idea

Maybe a 10.3mm dovetail would do both well... Hmmmm

Mark

Alstone · Moderator & Site Supporter

The thing is make sure what size of quality mount you can get, over here there are 11-13 mm mount's and 3/8"-11mm, and the thing is that you want the scope exactly over the barrel centre line, otherwise it will only zero at one place without adjusting the windage.

So make sure that the mount is for a set size and not a universal one, other wise if you are shooting using the over shoot or under shoot of a scope, or for Field Target you will have problems.

The diffrence between 11mm and 3/8" is 1/19" of an inch so this can push a scope way off line. I think donec confused his mm with his "". Razz

Al

Slavia · Moderator

I got curious, so I started looking around for dovetail standards. Nothing on the SAAMI site (Sporting Arms and Ammunition Institute). In fact, nothing anywhere that I could find. I did find three people that claim they don't exist:
http://www.trackofthewolf.com/categories/partdetail.aspx?catid=15&subid=86&styleid=306&partnum=labor-ds&AspxAutoDetectCookieSupport=1&as=1
http://www.practicalmachinist.com/vb/general/dovetail-dimensions-147955/
http://www.pyramydair.com/blog/2007/03/11mm-scope-dovetails-why-do-they.html

AirGunEric · Site Admin

donec · Senior Member

rsterne · Moderator

Assuming the scope mount is rigid on one side, and movable on the other (all are, AFAIK).... and that the grooves are too wide/narrow by 0.06".... the scope would only be 0.03" off the centerline of the barrel.... If the gun is sighted in at 25 yards.... it will be the same amount off (0.03") to the opposite side at 50 yards....

If you are going to be shooting at 50 to 100 yards, you will probably sight in at 50 yards at a minimum.... again, dead on a 50 yards, you would be off 0.03" at 100 yards....

Basically, who cares?.... Rolling Eyes

Bob

Alstone · Moderator & Site Supporter

The problem with most mounts is that they are all different, take for instance an 11mm mount with one fixed side these invariably wider so that they will accommodate a 3/8”, 12mm, or 13mm rail, so it depends how far from centre the fixed side is, also where it is measured from.

I have a lot of different mounts and some 11mm are up to 2mm off centre and it does make a difference especially for FT shooting, the only set of mounts I have that are perfect are a pair of self centring ones, but expensive.

Al

i8dirt · New Member

OK, I understand the nuances of off centre alignment now. Thank you.

I have found in an Anschuetz brochure, they use 11mm(at the widest part) by 60 degrees. No mention of how deep the dovetail. They also have a list of mounts to use. The Anschuetz is similar to the Air arms TX200 (11mm X 60deg X 1mm measured dovetail by Al). Thats two that are "consistent".

Some clarification on the 3/8 mount... Is that 3/8 (9.525mm) in the narrowest part of the dovetail or at the widest, I have seen conflicting info.

Have some 11mm rings coming in the post, will machine a test mockup to test how well it fits and centres.
Mark