Can anyone kindly advise on design dimensions of these chokes please?
I have a multichoke B525 sporter 1 and was thinking of obtaining some additional chokes for the skeet range. It was proofed at 18.7mm (0.736") both tubes, and still measures that. So some degree of over/back boring present. I have a standard set of Browning chokes at 1/4, 1/2, 3/4 and full UK sizing.
On inspection and with chokes installed, i note a distinct step at the junction of the breech end of the chokes and the muzzle end of the bores (pre-choke) All 4 chokes measure the same 0.750" bore at the breech end and taper according to the particular choke size. Please see attached NTS drawing.

So to my queries, the difference in bore diameter between each end of the chokes seem to conform approx to the expected constriction for each choke size ie 10, 20, 30 & 40 thou, however would the previously mentioned step not negate this? or does the conventional method of choke measuring not apply to invector plus chokes with over-bored tubes and the choke is determined purely on pellet count % in the circle at set yards?
I have not pattern tested any of the chokes, but would like to know if the step should be there by design?
I usually shoot antique muzzle loaders and early breech loading hammer guns, so removable chokes are new to me!
Many thanks.

Sorry to come in on Wootang's interesting question but it is along the same lines; can Browning Invector Plus Chokes be used in Winchester SX4 semi autos too? Lagopus…..

The 'step' is required to some degree on all screw in choke systems. There's also a bevel there.

This is necessary for safety, to keep gas from getting behind the choke tube and blowing things up. It also keeps lead and wad material from shaving and accumulating at the junction and acting as an obstruction.

This results in some 'jug' effect and varies considerably by manufacturer.

In general, screw in chokes shoot tighter than marked.

That said, factory supplied Invector+ (flush length) have a poor reputation in constrictions of modified or tighter. The various extended aftermarket chokes for this system are a HUGE improvement. The 'Midas' chokes shoot way better than flush ones and are rumored to be made by Briley.

For skeet in my Invector+ guns I use Briley chokes marked 'Cylinder'. There is still some effective choke constriction in those chokes because of the 'jug' section that's just part of the design. They work very well for skeet.

Winchester shows the SX4 as equipped with Invector+.

So, yes, Browning chokes will work too.

As will the various aftermarket chokes made for Invector Plus.

Good illustration of the step



It appears the tube is not however fully seated, allowing burnt power debris to accumulate in the gap, and with enough build up, blow out the tube

This is more likely from a dropped tube with bent skirt

Thanks guys, interesting explanations as to why the "step" is there. The greater the step i would guess the bigger the discepancy in actual to marked choke performance?
Sounds like some "jugging" is occuring with the design of these chokes, which is why the maths doesn't add up.
I would normally shoot UK 1/4 and 1/2 (US imp cyl and mod) on sporting clays, but from reading this would UK imp cyl and 3/8 (US skt and light mod) chokes equate more to this?
And for skeet, cylinder and cylinder seems the way to go?
Appreciating all you input.

Only the pattern board knows.....

That's about right.

It depends on the length of the choke 'leade' (for lack of a better word) as to how much jug effect you might observe.

Invector+ is a good sturdy system, at least the threads are not under the choke constriction like Beretta did with the Mobil Choke.

Not every mistake results in a blown barrel either. I once changed out a Beretta Optima choke at a sporting clays station, got distracted, and forgot to tighten it down. I shot 8 targets with it held in the barrel of the 391 by about 2 threads. No damage. My lucky day I guess.

Another time my shooting partner did the same thing with the choke just inserted and not threaded at all. I watched the choke sail off, kept my eye on it, and we walked right out and picked it up.

Shotgunjones, thanks for the info. I fairly recently bought an SX4 for vermin at work and it only came with three choke tubes. I already had some Browning Invector Plus choke tubes that I bought in a box of bits at an auction. The SX4 lacks a full choke tube in the package so now I can tighten up when needed. It looked to fit and I couldn't see any join so suspected that would be the case. Thanks again and apologies to Wootang for coming in on his similar topic. Lagopus…..

No problem Lagopus, glad my OP helped you out. If you have any invector + cylinder and skeet tubes you don't require, please PM me as i see you are also in the UK.

Thanks to Shotgunjones for the "leade" theory, ie the point up the choke taper that the shot column hits before being constricted (if it doesn't immediately expand upon passing the step?). Thinking about that and checking my choke dimensions, i see that the lighter chokes have a greater than expected total restriction, whereas the tighter ones do not. Could this explain why the tighter chokes perhaps do not perform so well?
Does anyone have a skeet and a cylinder invector + choke they could measure to add information to this?

I have a number of Invector+ I'll measure for you.

The 'standard' bore has been said to be .741 or .737 depending on who you read. They vary. It's just the way it is. Browning has been taken to task on this. They state a tolerance of -.003 from .741. They vary more than that.

1. BT-99 circa 2006. .736"
2. Cynergy 2004. .737" both.
3. CXS 2019. .735" both.

Factory supplied flush chokes referencing the 'for lead' marking.

1. Mod: Tapers back to bore in about 1.25". Tapers to .726 with about 1/2" of parallel.

2. IC: Similar, .733"

3: Skeet: Similar, .733", so identical to the IC.

The IC is a black finish and came with one of the guns. The skeet chokes (I bought a pair before I knew better) are silver finish and may or may not be stainless. They are Browning branded.

Briley flush mount CYL: Gently taper to .738", about 3/8" of parallel.

Briley extended MOD: .719". This a GREAT trap choke in the BT-99 back to 22 yards.

Briley extended IM: .713". Quite effective at 27 yard trap, and even breaks the ones I point correctly from the picnic table which is about 35 yards behind the trap. I see no performance difference between this rig and a Beretta trap gun with their typical .722 bore and .037 of hard choke. I've never seen the need to buy a Briley full choke for INV+.

Briley extended IC: .728"

Carlson extended CYL: .739". These have a slightly longer parallel than the Brileys.

Carlson extended LM: .725"

Carlsons extended SKT: .733"

Browning Midas Full: .704

Browning Midas MOD: .719

Browning Midas IC: .731

The Browning flush 'Full' that came with the trap gun was either given away or disposed of in disgust. It was a lousy choke.

That's the report.

Good luck.

Thankyou Shotgunjones for taking the time and trouble to supply this extensive information.
Found in Brownings blurb about 0.742" being "the ideal interior barrel diameter for back-bored 12 gauge", equating to 18.85mm. so these tubes would probably be proof stamped at 18.8

Are all of your chokes generally 0.750" bore at the threaded (breech) end as mine? or does a particular manufacturer tend to have a smaller bore at the breech end of its chokes? which would then reduce the step in my 18.7 mm gun
It seems the factory Browning flush chokes need tossing in the bin!
Thanks again

They all seem similar as far as initial diameter.

If you can't get Briley or Carlson's there, my brother uses the Browning Midas in 'cylinder' for skeet to good effect.

As mentioned, those are apparently made by Briley but not identical internally to their own brand. They just do what Browning specs.

They're also black with a snazzy gold ring and of course they cost a fortune. My CXS came with 3 of them instead of the flush ones, thankfully. They shoot OK.

Just a brief update on my quest for aftermarket chokes for my B525.
Briley's are available in the UK but couldn't find them in stock in the sizes and types that i was after. Decided to try Teague precision who are based in UK. Liked the look of their extended but unported type in stainless and ordered a cylinder, skeet and 3/8 (light mod)for my 18.7mm (0.736") bores. They arrived today, finished very nicely inside and out and with a good knurled extended section big enough to screw in by hand so no need for their special tapered tool.
Some measurements taken:

size/entry/exit/nom restriction/Actual restriction(bore - exit)

Cyl/0.752"/0.735"/0.000"/0.001"
Skt/0.752"/0.729"/0.005"/0.007"
3/8/0.752"/0.721"/0.015"/0.015"

So it would seem for Teague, and perhaps other makers?, the actual restriction difference between barrel bore and choke exit pretty well matches the nominal restriction for that size choke. For more open chokes anyway.
The "step" still remains, so therefore still the potential for jugging effect, so it will be interesting to see if they perform true to size or tighter. I have dropped from 1/4 and 1/2 to skt and 3/8 anticipating them to be tighter.

Glad you found what you were looking for.

I take it Teague does not use notches for torque.

A "soft jaw" pliers works pretty well for that and beats the conical wrench.

Yep, we will see how good they are in due course!
No notches in these extended chokes, rely on friction fit with the
"special" key only, but you can get them sufficiently tight by hand on the knurling, and if too tight to remove, the pliers would do the job i'm sure!